process_madvise currently requires ptrace attach capability. PTRACE_MODE_ATTACH gives one process complete control over another process. It effectively removes the security boundary between the two processes (in one direction). Granting ptrace attach capability even to a system process is considered dangerous since it creates an attack surface. This severely limits the usage of this API. The operations process_madvise can perform do not affect the correctness of the operation of the target process; they only affect where the data is physically located (and therefore, how fast it can be accessed). What we want is the ability for one process to influence another process in order to optimize performance across the entire system while leaving the security boundary intact. Replace PTRACE_MODE_ATTACH with a combination of PTRACE_MODE_READ and CAP_SYS_NICE. PTRACE_MODE_READ to prevent leaking ASLR metadata and CAP_SYS_NICE for influencing process performance.
Cc: stable@vger.kernel.org # 5.10+ Signed-off-by: Suren Baghdasaryan surenb@google.com Reviewed-by: Kees Cook keescook@chromium.org Acked-by: Minchan Kim minchan@kernel.org Acked-by: David Rientjes rientjes@google.com --- changes in v3 - Added Reviewed-by: Kees Cook keescook@chromium.org - Created man page for process_madvise per Andrew's request: https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/commit/?id=a144f... - cc'ed stable@vger.kernel.org # 5.10+ per Andrew's request - cc'ed linux-security-module@vger.kernel.org per James Morris's request
mm/madvise.c | 13 ++++++++++++- 1 file changed, 12 insertions(+), 1 deletion(-)
diff --git a/mm/madvise.c b/mm/madvise.c index df692d2e35d4..01fef79ac761 100644 --- a/mm/madvise.c +++ b/mm/madvise.c @@ -1198,12 +1198,22 @@ SYSCALL_DEFINE5(process_madvise, int, pidfd, const struct iovec __user *, vec, goto release_task; }
- mm = mm_access(task, PTRACE_MODE_ATTACH_FSCREDS); + /* Require PTRACE_MODE_READ to avoid leaking ASLR metadata. */ + mm = mm_access(task, PTRACE_MODE_READ_FSCREDS); if (IS_ERR_OR_NULL(mm)) { ret = IS_ERR(mm) ? PTR_ERR(mm) : -ESRCH; goto release_task; }
+ /* + * Require CAP_SYS_NICE for influencing process performance. Note that + * only non-destructive hints are currently supported. + */ + if (!capable(CAP_SYS_NICE)) { + ret = -EPERM; + goto release_mm; + } + total_len = iov_iter_count(&iter);
while (iov_iter_count(&iter)) { @@ -1218,6 +1228,7 @@ SYSCALL_DEFINE5(process_madvise, int, pidfd, const struct iovec __user *, vec, if (ret == 0) ret = total_len - iov_iter_count(&iter);
+release_mm: mmput(mm); release_task: put_task_struct(task);
On Wed, Mar 3, 2021 at 10:58 AM Suren Baghdasaryan surenb@google.com wrote:
process_madvise currently requires ptrace attach capability. PTRACE_MODE_ATTACH gives one process complete control over another process. It effectively removes the security boundary between the two processes (in one direction). Granting ptrace attach capability even to a system process is considered dangerous since it creates an attack surface. This severely limits the usage of this API. The operations process_madvise can perform do not affect the correctness of the operation of the target process; they only affect where the data is physically located (and therefore, how fast it can be accessed). What we want is the ability for one process to influence another process in order to optimize performance across the entire system while leaving the security boundary intact. Replace PTRACE_MODE_ATTACH with a combination of PTRACE_MODE_READ and CAP_SYS_NICE. PTRACE_MODE_READ to prevent leaking ASLR metadata and CAP_SYS_NICE for influencing process performance.
Cc: stable@vger.kernel.org # 5.10+ Signed-off-by: Suren Baghdasaryan surenb@google.com Reviewed-by: Kees Cook keescook@chromium.org Acked-by: Minchan Kim minchan@kernel.org Acked-by: David Rientjes rientjes@google.com
changes in v3
- Added Reviewed-by: Kees Cook keescook@chromium.org
- Created man page for process_madvise per Andrew's request: https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/commit/?id=a144f...
- cc'ed stable@vger.kernel.org # 5.10+ per Andrew's request
- cc'ed linux-security-module@vger.kernel.org per James Morris's request
mm/madvise.c | 13 ++++++++++++- 1 file changed, 12 insertions(+), 1 deletion(-)
diff --git a/mm/madvise.c b/mm/madvise.c index df692d2e35d4..01fef79ac761 100644 --- a/mm/madvise.c +++ b/mm/madvise.c @@ -1198,12 +1198,22 @@ SYSCALL_DEFINE5(process_madvise, int, pidfd, const struct iovec __user *, vec, goto release_task; }
mm = mm_access(task, PTRACE_MODE_ATTACH_FSCREDS);
/* Require PTRACE_MODE_READ to avoid leaking ASLR metadata. */mm = mm_access(task, PTRACE_MODE_READ_FSCREDS); if (IS_ERR_OR_NULL(mm)) { ret = IS_ERR(mm) ? PTR_ERR(mm) : -ESRCH; goto release_task; }/** Require CAP_SYS_NICE for influencing process performance. Note that* only non-destructive hints are currently supported.
How is non-destructive defined? Is MADV_DONTNEED non-destructive?
*/if (!capable(CAP_SYS_NICE)) {ret = -EPERM;goto release_mm;}total_len = iov_iter_count(&iter); while (iov_iter_count(&iter)) {@@ -1218,6 +1228,7 @@ SYSCALL_DEFINE5(process_madvise, int, pidfd, const struct iovec __user *, vec, if (ret == 0) ret = total_len - iov_iter_count(&iter);
+release_mm: mmput(mm); release_task: put_task_struct(task); -- 2.30.1.766.gb4fecdf3b7-goog
On Wed, Mar 3, 2021 at 3:17 PM Shakeel Butt shakeelb@google.com wrote:
On Wed, Mar 3, 2021 at 10:58 AM Suren Baghdasaryan surenb@google.com wrote:
process_madvise currently requires ptrace attach capability. PTRACE_MODE_ATTACH gives one process complete control over another process. It effectively removes the security boundary between the two processes (in one direction). Granting ptrace attach capability even to a system process is considered dangerous since it creates an attack surface. This severely limits the usage of this API. The operations process_madvise can perform do not affect the correctness of the operation of the target process; they only affect where the data is physically located (and therefore, how fast it can be accessed). What we want is the ability for one process to influence another process in order to optimize performance across the entire system while leaving the security boundary intact. Replace PTRACE_MODE_ATTACH with a combination of PTRACE_MODE_READ and CAP_SYS_NICE. PTRACE_MODE_READ to prevent leaking ASLR metadata and CAP_SYS_NICE for influencing process performance.
Cc: stable@vger.kernel.org # 5.10+ Signed-off-by: Suren Baghdasaryan surenb@google.com Reviewed-by: Kees Cook keescook@chromium.org Acked-by: Minchan Kim minchan@kernel.org Acked-by: David Rientjes rientjes@google.com
changes in v3
- Added Reviewed-by: Kees Cook keescook@chromium.org
- Created man page for process_madvise per Andrew's request: https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/commit/?id=a144f...
- cc'ed stable@vger.kernel.org # 5.10+ per Andrew's request
- cc'ed linux-security-module@vger.kernel.org per James Morris's request
mm/madvise.c | 13 ++++++++++++- 1 file changed, 12 insertions(+), 1 deletion(-)
diff --git a/mm/madvise.c b/mm/madvise.c index df692d2e35d4..01fef79ac761 100644 --- a/mm/madvise.c +++ b/mm/madvise.c @@ -1198,12 +1198,22 @@ SYSCALL_DEFINE5(process_madvise, int, pidfd, const struct iovec __user *, vec, goto release_task; }
mm = mm_access(task, PTRACE_MODE_ATTACH_FSCREDS);
/* Require PTRACE_MODE_READ to avoid leaking ASLR metadata. */mm = mm_access(task, PTRACE_MODE_READ_FSCREDS); if (IS_ERR_OR_NULL(mm)) { ret = IS_ERR(mm) ? PTR_ERR(mm) : -ESRCH; goto release_task; }/** Require CAP_SYS_NICE for influencing process performance. Note that* only non-destructive hints are currently supported.How is non-destructive defined? Is MADV_DONTNEED non-destructive?
Non-destructive in this context means the data is not lost and can be recovered. I follow the logic described in https://lwn.net/Articles/794704/ where Minchan was introducing MADV_COLD and MADV_PAGEOUT as non-destructive versions of MADV_FREE and MADV_DONTNEED. Following that logic, MADV_FREE and MADV_DONTNEED would be considered destructive hints. Note that process_madvise_behavior_valid() allows only MADV_COLD and MADV_PAGEOUT at the moment, which are both non-destructive.
*/if (!capable(CAP_SYS_NICE)) {ret = -EPERM;goto release_mm;}total_len = iov_iter_count(&iter); while (iov_iter_count(&iter)) {@@ -1218,6 +1228,7 @@ SYSCALL_DEFINE5(process_madvise, int, pidfd, const struct iovec __user *, vec, if (ret == 0) ret = total_len - iov_iter_count(&iter);
+release_mm: mmput(mm); release_task: put_task_struct(task); -- 2.30.1.766.gb4fecdf3b7-goog
On Wed, Mar 3, 2021 at 3:34 PM Suren Baghdasaryan surenb@google.com wrote:
On Wed, Mar 3, 2021 at 3:17 PM Shakeel Butt shakeelb@google.com wrote:
On Wed, Mar 3, 2021 at 10:58 AM Suren Baghdasaryan surenb@google.com wrote:
process_madvise currently requires ptrace attach capability. PTRACE_MODE_ATTACH gives one process complete control over another process. It effectively removes the security boundary between the two processes (in one direction). Granting ptrace attach capability even to a system process is considered dangerous since it creates an attack surface. This severely limits the usage of this API. The operations process_madvise can perform do not affect the correctness of the operation of the target process; they only affect where the data is physically located (and therefore, how fast it can be accessed). What we want is the ability for one process to influence another process in order to optimize performance across the entire system while leaving the security boundary intact. Replace PTRACE_MODE_ATTACH with a combination of PTRACE_MODE_READ and CAP_SYS_NICE. PTRACE_MODE_READ to prevent leaking ASLR metadata and CAP_SYS_NICE for influencing process performance.
Cc: stable@vger.kernel.org # 5.10+ Signed-off-by: Suren Baghdasaryan surenb@google.com Reviewed-by: Kees Cook keescook@chromium.org Acked-by: Minchan Kim minchan@kernel.org Acked-by: David Rientjes rientjes@google.com
changes in v3
- Added Reviewed-by: Kees Cook keescook@chromium.org
- Created man page for process_madvise per Andrew's request: https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/commit/?id=a144f...
- cc'ed stable@vger.kernel.org # 5.10+ per Andrew's request
- cc'ed linux-security-module@vger.kernel.org per James Morris's request
mm/madvise.c | 13 ++++++++++++- 1 file changed, 12 insertions(+), 1 deletion(-)
diff --git a/mm/madvise.c b/mm/madvise.c index df692d2e35d4..01fef79ac761 100644 --- a/mm/madvise.c +++ b/mm/madvise.c @@ -1198,12 +1198,22 @@ SYSCALL_DEFINE5(process_madvise, int, pidfd, const struct iovec __user *, vec, goto release_task; }
mm = mm_access(task, PTRACE_MODE_ATTACH_FSCREDS);
/* Require PTRACE_MODE_READ to avoid leaking ASLR metadata. */mm = mm_access(task, PTRACE_MODE_READ_FSCREDS); if (IS_ERR_OR_NULL(mm)) { ret = IS_ERR(mm) ? PTR_ERR(mm) : -ESRCH; goto release_task; }/** Require CAP_SYS_NICE for influencing process performance. Note that* only non-destructive hints are currently supported.How is non-destructive defined? Is MADV_DONTNEED non-destructive?
Non-destructive in this context means the data is not lost and can be recovered. I follow the logic described in https://lwn.net/Articles/794704/ where Minchan was introducing MADV_COLD and MADV_PAGEOUT as non-destructive versions of MADV_FREE and MADV_DONTNEED. Following that logic, MADV_FREE and MADV_DONTNEED would be considered destructive hints. Note that process_madvise_behavior_valid() allows only MADV_COLD and MADV_PAGEOUT at the moment, which are both non-destructive.
There is a plan to support MADV_DONTNEED for this syscall. Do we need to change these access checks again with that support?
On Wed, Mar 3, 2021 at 4:04 PM Shakeel Butt shakeelb@google.com wrote:
On Wed, Mar 3, 2021 at 3:34 PM Suren Baghdasaryan surenb@google.com wrote:
On Wed, Mar 3, 2021 at 3:17 PM Shakeel Butt shakeelb@google.com wrote:
On Wed, Mar 3, 2021 at 10:58 AM Suren Baghdasaryan surenb@google.com wrote:
process_madvise currently requires ptrace attach capability. PTRACE_MODE_ATTACH gives one process complete control over another process. It effectively removes the security boundary between the two processes (in one direction). Granting ptrace attach capability even to a system process is considered dangerous since it creates an attack surface. This severely limits the usage of this API. The operations process_madvise can perform do not affect the correctness of the operation of the target process; they only affect where the data is physically located (and therefore, how fast it can be accessed). What we want is the ability for one process to influence another process in order to optimize performance across the entire system while leaving the security boundary intact. Replace PTRACE_MODE_ATTACH with a combination of PTRACE_MODE_READ and CAP_SYS_NICE. PTRACE_MODE_READ to prevent leaking ASLR metadata and CAP_SYS_NICE for influencing process performance.
Cc: stable@vger.kernel.org # 5.10+ Signed-off-by: Suren Baghdasaryan surenb@google.com Reviewed-by: Kees Cook keescook@chromium.org Acked-by: Minchan Kim minchan@kernel.org Acked-by: David Rientjes rientjes@google.com
changes in v3
- Added Reviewed-by: Kees Cook keescook@chromium.org
- Created man page for process_madvise per Andrew's request: https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/commit/?id=a144f...
- cc'ed stable@vger.kernel.org # 5.10+ per Andrew's request
- cc'ed linux-security-module@vger.kernel.org per James Morris's request
mm/madvise.c | 13 ++++++++++++- 1 file changed, 12 insertions(+), 1 deletion(-)
diff --git a/mm/madvise.c b/mm/madvise.c index df692d2e35d4..01fef79ac761 100644 --- a/mm/madvise.c +++ b/mm/madvise.c @@ -1198,12 +1198,22 @@ SYSCALL_DEFINE5(process_madvise, int, pidfd, const struct iovec __user *, vec, goto release_task; }
mm = mm_access(task, PTRACE_MODE_ATTACH_FSCREDS);
/* Require PTRACE_MODE_READ to avoid leaking ASLR metadata. */mm = mm_access(task, PTRACE_MODE_READ_FSCREDS); if (IS_ERR_OR_NULL(mm)) { ret = IS_ERR(mm) ? PTR_ERR(mm) : -ESRCH; goto release_task; }/** Require CAP_SYS_NICE for influencing process performance. Note that* only non-destructive hints are currently supported.How is non-destructive defined? Is MADV_DONTNEED non-destructive?
Non-destructive in this context means the data is not lost and can be recovered. I follow the logic described in https://lwn.net/Articles/794704/ where Minchan was introducing MADV_COLD and MADV_PAGEOUT as non-destructive versions of MADV_FREE and MADV_DONTNEED. Following that logic, MADV_FREE and MADV_DONTNEED would be considered destructive hints. Note that process_madvise_behavior_valid() allows only MADV_COLD and MADV_PAGEOUT at the moment, which are both non-destructive.
There is a plan to support MADV_DONTNEED for this syscall. Do we need to change these access checks again with that support?
I think so. Destructive hints affect the data, so we will probably need stricter checks for those hints.
On 04.03.21 01:03, Shakeel Butt wrote:
On Wed, Mar 3, 2021 at 3:34 PM Suren Baghdasaryan surenb@google.com wrote:
On Wed, Mar 3, 2021 at 3:17 PM Shakeel Butt shakeelb@google.com wrote:
On Wed, Mar 3, 2021 at 10:58 AM Suren Baghdasaryan surenb@google.com wrote:
process_madvise currently requires ptrace attach capability. PTRACE_MODE_ATTACH gives one process complete control over another process. It effectively removes the security boundary between the two processes (in one direction). Granting ptrace attach capability even to a system process is considered dangerous since it creates an attack surface. This severely limits the usage of this API. The operations process_madvise can perform do not affect the correctness of the operation of the target process; they only affect where the data is physically located (and therefore, how fast it can be accessed). What we want is the ability for one process to influence another process in order to optimize performance across the entire system while leaving the security boundary intact. Replace PTRACE_MODE_ATTACH with a combination of PTRACE_MODE_READ and CAP_SYS_NICE. PTRACE_MODE_READ to prevent leaking ASLR metadata and CAP_SYS_NICE for influencing process performance.
Cc: stable@vger.kernel.org # 5.10+ Signed-off-by: Suren Baghdasaryan surenb@google.com Reviewed-by: Kees Cook keescook@chromium.org Acked-by: Minchan Kim minchan@kernel.org Acked-by: David Rientjes rientjes@google.com
changes in v3
Added Reviewed-by: Kees Cook keescook@chromium.org
Created man page for process_madvise per Andrew's request: https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/commit/?id=a144f...
cc'ed stable@vger.kernel.org # 5.10+ per Andrew's request
cc'ed linux-security-module@vger.kernel.org per James Morris's request
mm/madvise.c | 13 ++++++++++++- 1 file changed, 12 insertions(+), 1 deletion(-)
diff --git a/mm/madvise.c b/mm/madvise.c index df692d2e35d4..01fef79ac761 100644 --- a/mm/madvise.c +++ b/mm/madvise.c @@ -1198,12 +1198,22 @@ SYSCALL_DEFINE5(process_madvise, int, pidfd, const struct iovec __user *, vec, goto release_task; }
mm = mm_access(task, PTRACE_MODE_ATTACH_FSCREDS);
/* Require PTRACE_MODE_READ to avoid leaking ASLR metadata. */mm = mm_access(task, PTRACE_MODE_READ_FSCREDS); if (IS_ERR_OR_NULL(mm)) { ret = IS_ERR(mm) ? PTR_ERR(mm) : -ESRCH; goto release_task; }/** Require CAP_SYS_NICE for influencing process performance. Note that* only non-destructive hints are currently supported.How is non-destructive defined? Is MADV_DONTNEED non-destructive?
Non-destructive in this context means the data is not lost and can be recovered. I follow the logic described in https://lwn.net/Articles/794704/ where Minchan was introducing MADV_COLD and MADV_PAGEOUT as non-destructive versions of MADV_FREE and MADV_DONTNEED. Following that logic, MADV_FREE and MADV_DONTNEED would be considered destructive hints. Note that process_madvise_behavior_valid() allows only MADV_COLD and MADV_PAGEOUT at the moment, which are both non-destructive.
There is a plan to support MADV_DONTNEED for this syscall. Do we need to change these access checks again with that support?
Eh, I absolutely don't think letting another process discard memory in another process' address space is a good idea. The target process can observe that easily and might even run into real issues.
What's the use case?
On Fri, Mar 5, 2021 at 9:37 AM David Hildenbrand david@redhat.com wrote:
On 04.03.21 01:03, Shakeel Butt wrote:
On Wed, Mar 3, 2021 at 3:34 PM Suren Baghdasaryan surenb@google.com wrote:
On Wed, Mar 3, 2021 at 3:17 PM Shakeel Butt shakeelb@google.com wrote:
On Wed, Mar 3, 2021 at 10:58 AM Suren Baghdasaryan surenb@google.com wrote:
process_madvise currently requires ptrace attach capability. PTRACE_MODE_ATTACH gives one process complete control over another process. It effectively removes the security boundary between the two processes (in one direction). Granting ptrace attach capability even to a system process is considered dangerous since it creates an attack surface. This severely limits the usage of this API. The operations process_madvise can perform do not affect the correctness of the operation of the target process; they only affect where the data is physically located (and therefore, how fast it can be accessed). What we want is the ability for one process to influence another process in order to optimize performance across the entire system while leaving the security boundary intact. Replace PTRACE_MODE_ATTACH with a combination of PTRACE_MODE_READ and CAP_SYS_NICE. PTRACE_MODE_READ to prevent leaking ASLR metadata and CAP_SYS_NICE for influencing process performance.
Cc: stable@vger.kernel.org # 5.10+ Signed-off-by: Suren Baghdasaryan surenb@google.com Reviewed-by: Kees Cook keescook@chromium.org Acked-by: Minchan Kim minchan@kernel.org Acked-by: David Rientjes rientjes@google.com
changes in v3
Added Reviewed-by: Kees Cook keescook@chromium.org
Created man page for process_madvise per Andrew's request: https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/commit/?id=a144f...
cc'ed stable@vger.kernel.org # 5.10+ per Andrew's request
cc'ed linux-security-module@vger.kernel.org per James Morris's request
mm/madvise.c | 13 ++++++++++++- 1 file changed, 12 insertions(+), 1 deletion(-)
diff --git a/mm/madvise.c b/mm/madvise.c index df692d2e35d4..01fef79ac761 100644 --- a/mm/madvise.c +++ b/mm/madvise.c @@ -1198,12 +1198,22 @@ SYSCALL_DEFINE5(process_madvise, int, pidfd, const struct iovec __user *, vec, goto release_task; }
mm = mm_access(task, PTRACE_MODE_ATTACH_FSCREDS);
/* Require PTRACE_MODE_READ to avoid leaking ASLR metadata. */mm = mm_access(task, PTRACE_MODE_READ_FSCREDS); if (IS_ERR_OR_NULL(mm)) { ret = IS_ERR(mm) ? PTR_ERR(mm) : -ESRCH; goto release_task; }/** Require CAP_SYS_NICE for influencing process performance. Note that* only non-destructive hints are currently supported.How is non-destructive defined? Is MADV_DONTNEED non-destructive?
Non-destructive in this context means the data is not lost and can be recovered. I follow the logic described in https://lwn.net/Articles/794704/ where Minchan was introducing MADV_COLD and MADV_PAGEOUT as non-destructive versions of MADV_FREE and MADV_DONTNEED. Following that logic, MADV_FREE and MADV_DONTNEED would be considered destructive hints. Note that process_madvise_behavior_valid() allows only MADV_COLD and MADV_PAGEOUT at the moment, which are both non-destructive.
There is a plan to support MADV_DONTNEED for this syscall. Do we need to change these access checks again with that support?
Eh, I absolutely don't think letting another process discard memory in another process' address space is a good idea. The target process can observe that easily and might even run into real issues.
What's the use case?
Userspace oom reaper. Please look at https://lore.kernel.org/linux-api/20201014183943.GA1489464@google.com/T/
On 05.03.21 18:45, Shakeel Butt wrote:
On Fri, Mar 5, 2021 at 9:37 AM David Hildenbrand david@redhat.com wrote:
On 04.03.21 01:03, Shakeel Butt wrote:
On Wed, Mar 3, 2021 at 3:34 PM Suren Baghdasaryan surenb@google.com wrote:
On Wed, Mar 3, 2021 at 3:17 PM Shakeel Butt shakeelb@google.com wrote:
On Wed, Mar 3, 2021 at 10:58 AM Suren Baghdasaryan surenb@google.com wrote:
process_madvise currently requires ptrace attach capability. PTRACE_MODE_ATTACH gives one process complete control over another process. It effectively removes the security boundary between the two processes (in one direction). Granting ptrace attach capability even to a system process is considered dangerous since it creates an attack surface. This severely limits the usage of this API. The operations process_madvise can perform do not affect the correctness of the operation of the target process; they only affect where the data is physically located (and therefore, how fast it can be accessed). What we want is the ability for one process to influence another process in order to optimize performance across the entire system while leaving the security boundary intact. Replace PTRACE_MODE_ATTACH with a combination of PTRACE_MODE_READ and CAP_SYS_NICE. PTRACE_MODE_READ to prevent leaking ASLR metadata and CAP_SYS_NICE for influencing process performance.
Cc: stable@vger.kernel.org # 5.10+ Signed-off-by: Suren Baghdasaryan surenb@google.com Reviewed-by: Kees Cook keescook@chromium.org Acked-by: Minchan Kim minchan@kernel.org Acked-by: David Rientjes rientjes@google.com
changes in v3
Added Reviewed-by: Kees Cook keescook@chromium.org
Created man page for process_madvise per Andrew's request: https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/commit/?id=a144f...
cc'ed stable@vger.kernel.org # 5.10+ per Andrew's request
cc'ed linux-security-module@vger.kernel.org per James Morris's request
mm/madvise.c | 13 ++++++++++++- 1 file changed, 12 insertions(+), 1 deletion(-)
diff --git a/mm/madvise.c b/mm/madvise.c index df692d2e35d4..01fef79ac761 100644 --- a/mm/madvise.c +++ b/mm/madvise.c @@ -1198,12 +1198,22 @@ SYSCALL_DEFINE5(process_madvise, int, pidfd, const struct iovec __user *, vec, goto release_task; }
mm = mm_access(task, PTRACE_MODE_ATTACH_FSCREDS);
/* Require PTRACE_MODE_READ to avoid leaking ASLR metadata. */mm = mm_access(task, PTRACE_MODE_READ_FSCREDS); if (IS_ERR_OR_NULL(mm)) { ret = IS_ERR(mm) ? PTR_ERR(mm) : -ESRCH; goto release_task; }/** Require CAP_SYS_NICE for influencing process performance. Note that* only non-destructive hints are currently supported.How is non-destructive defined? Is MADV_DONTNEED non-destructive?
Non-destructive in this context means the data is not lost and can be recovered. I follow the logic described in https://lwn.net/Articles/794704/ where Minchan was introducing MADV_COLD and MADV_PAGEOUT as non-destructive versions of MADV_FREE and MADV_DONTNEED. Following that logic, MADV_FREE and MADV_DONTNEED would be considered destructive hints. Note that process_madvise_behavior_valid() allows only MADV_COLD and MADV_PAGEOUT at the moment, which are both non-destructive.
There is a plan to support MADV_DONTNEED for this syscall. Do we need to change these access checks again with that support?
Eh, I absolutely don't think letting another process discard memory in another process' address space is a good idea. The target process can observe that easily and might even run into real issues.
What's the use case?
Userspace oom reaper. Please look at https://lore.kernel.org/linux-api/20201014183943.GA1489464@google.com/T/
Thanks, somehow I missed that (not that it really changed my opinion on the approach while skimming over the discussion :) will have a more detailed look)
On Fri, Mar 5, 2021 at 9:52 AM David Hildenbrand david@redhat.com wrote:
On 05.03.21 18:45, Shakeel Butt wrote:
On Fri, Mar 5, 2021 at 9:37 AM David Hildenbrand david@redhat.com wrote:
On 04.03.21 01:03, Shakeel Butt wrote:
On Wed, Mar 3, 2021 at 3:34 PM Suren Baghdasaryan surenb@google.com wrote:
On Wed, Mar 3, 2021 at 3:17 PM Shakeel Butt shakeelb@google.com wrote:
On Wed, Mar 3, 2021 at 10:58 AM Suren Baghdasaryan surenb@google.com wrote: > > process_madvise currently requires ptrace attach capability. > PTRACE_MODE_ATTACH gives one process complete control over another > process. It effectively removes the security boundary between the > two processes (in one direction). Granting ptrace attach capability > even to a system process is considered dangerous since it creates an > attack surface. This severely limits the usage of this API. > The operations process_madvise can perform do not affect the correctness > of the operation of the target process; they only affect where the data > is physically located (and therefore, how fast it can be accessed). > What we want is the ability for one process to influence another process > in order to optimize performance across the entire system while leaving > the security boundary intact. > Replace PTRACE_MODE_ATTACH with a combination of PTRACE_MODE_READ > and CAP_SYS_NICE. PTRACE_MODE_READ to prevent leaking ASLR metadata > and CAP_SYS_NICE for influencing process performance. > > Cc: stable@vger.kernel.org # 5.10+ > Signed-off-by: Suren Baghdasaryan surenb@google.com > Reviewed-by: Kees Cook keescook@chromium.org > Acked-by: Minchan Kim minchan@kernel.org > Acked-by: David Rientjes rientjes@google.com > --- > changes in v3 > - Added Reviewed-by: Kees Cook keescook@chromium.org > - Created man page for process_madvise per Andrew's request: https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/commit/?id=a144f... > - cc'ed stable@vger.kernel.org # 5.10+ per Andrew's request > - cc'ed linux-security-module@vger.kernel.org per James Morris's request > > mm/madvise.c | 13 ++++++++++++- > 1 file changed, 12 insertions(+), 1 deletion(-) > > diff --git a/mm/madvise.c b/mm/madvise.c > index df692d2e35d4..01fef79ac761 100644 > --- a/mm/madvise.c > +++ b/mm/madvise.c > @@ -1198,12 +1198,22 @@ SYSCALL_DEFINE5(process_madvise, int, pidfd, const struct iovec __user *, vec, > goto release_task; > } > > - mm = mm_access(task, PTRACE_MODE_ATTACH_FSCREDS); > + /* Require PTRACE_MODE_READ to avoid leaking ASLR metadata. */ > + mm = mm_access(task, PTRACE_MODE_READ_FSCREDS); > if (IS_ERR_OR_NULL(mm)) { > ret = IS_ERR(mm) ? PTR_ERR(mm) : -ESRCH; > goto release_task; > } > > + /* > + * Require CAP_SYS_NICE for influencing process performance. Note that > + * only non-destructive hints are currently supported.
How is non-destructive defined? Is MADV_DONTNEED non-destructive?
Non-destructive in this context means the data is not lost and can be recovered. I follow the logic described in https://lwn.net/Articles/794704/ where Minchan was introducing MADV_COLD and MADV_PAGEOUT as non-destructive versions of MADV_FREE and MADV_DONTNEED. Following that logic, MADV_FREE and MADV_DONTNEED would be considered destructive hints. Note that process_madvise_behavior_valid() allows only MADV_COLD and MADV_PAGEOUT at the moment, which are both non-destructive.
There is a plan to support MADV_DONTNEED for this syscall. Do we need to change these access checks again with that support?
Eh, I absolutely don't think letting another process discard memory in another process' address space is a good idea. The target process can observe that easily and might even run into real issues.
What's the use case?
Userspace oom reaper. Please look at https://lore.kernel.org/linux-api/20201014183943.GA1489464@google.com/T/
Thanks, somehow I missed that (not that it really changed my opinion on the approach while skimming over the discussion :) will have a more detailed look)
The latest version of that patchset is: https://lore.kernel.org/patchwork/patch/1344419/ Yeah, memory reaping is a special case when we are operating on a dying process to speed up the release of its memory. I don't know if for that particular case we need to make the checks stricter. It's a dying process anyway and the data is being destroyed. Allowing to speed up that process probably can still use CAP_SYS_NICE.
-- Thanks,
David / dhildenb
On 05.03.21 19:08, Suren Baghdasaryan wrote:
On Fri, Mar 5, 2021 at 9:52 AM David Hildenbrand david@redhat.com wrote:
On 05.03.21 18:45, Shakeel Butt wrote:
On Fri, Mar 5, 2021 at 9:37 AM David Hildenbrand david@redhat.com wrote:
On 04.03.21 01:03, Shakeel Butt wrote:
On Wed, Mar 3, 2021 at 3:34 PM Suren Baghdasaryan surenb@google.com wrote:
On Wed, Mar 3, 2021 at 3:17 PM Shakeel Butt shakeelb@google.com wrote: > > On Wed, Mar 3, 2021 at 10:58 AM Suren Baghdasaryan surenb@google.com wrote: >> >> process_madvise currently requires ptrace attach capability. >> PTRACE_MODE_ATTACH gives one process complete control over another >> process. It effectively removes the security boundary between the >> two processes (in one direction). Granting ptrace attach capability >> even to a system process is considered dangerous since it creates an >> attack surface. This severely limits the usage of this API. >> The operations process_madvise can perform do not affect the correctness >> of the operation of the target process; they only affect where the data >> is physically located (and therefore, how fast it can be accessed). >> What we want is the ability for one process to influence another process >> in order to optimize performance across the entire system while leaving >> the security boundary intact. >> Replace PTRACE_MODE_ATTACH with a combination of PTRACE_MODE_READ >> and CAP_SYS_NICE. PTRACE_MODE_READ to prevent leaking ASLR metadata >> and CAP_SYS_NICE for influencing process performance. >> >> Cc: stable@vger.kernel.org # 5.10+ >> Signed-off-by: Suren Baghdasaryan surenb@google.com >> Reviewed-by: Kees Cook keescook@chromium.org >> Acked-by: Minchan Kim minchan@kernel.org >> Acked-by: David Rientjes rientjes@google.com >> --- >> changes in v3 >> - Added Reviewed-by: Kees Cook keescook@chromium.org >> - Created man page for process_madvise per Andrew's request: https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/commit/?id=a144f... >> - cc'ed stable@vger.kernel.org # 5.10+ per Andrew's request >> - cc'ed linux-security-module@vger.kernel.org per James Morris's request >> >> mm/madvise.c | 13 ++++++++++++- >> 1 file changed, 12 insertions(+), 1 deletion(-) >> >> diff --git a/mm/madvise.c b/mm/madvise.c >> index df692d2e35d4..01fef79ac761 100644 >> --- a/mm/madvise.c >> +++ b/mm/madvise.c >> @@ -1198,12 +1198,22 @@ SYSCALL_DEFINE5(process_madvise, int, pidfd, const struct iovec __user *, vec, >> goto release_task; >> } >> >> - mm = mm_access(task, PTRACE_MODE_ATTACH_FSCREDS); >> + /* Require PTRACE_MODE_READ to avoid leaking ASLR metadata. */ >> + mm = mm_access(task, PTRACE_MODE_READ_FSCREDS); >> if (IS_ERR_OR_NULL(mm)) { >> ret = IS_ERR(mm) ? PTR_ERR(mm) : -ESRCH; >> goto release_task; >> } >> >> + /* >> + * Require CAP_SYS_NICE for influencing process performance. Note that >> + * only non-destructive hints are currently supported. > > How is non-destructive defined? Is MADV_DONTNEED non-destructive?
Non-destructive in this context means the data is not lost and can be recovered. I follow the logic described in https://lwn.net/Articles/794704/ where Minchan was introducing MADV_COLD and MADV_PAGEOUT as non-destructive versions of MADV_FREE and MADV_DONTNEED. Following that logic, MADV_FREE and MADV_DONTNEED would be considered destructive hints. Note that process_madvise_behavior_valid() allows only MADV_COLD and MADV_PAGEOUT at the moment, which are both non-destructive.
There is a plan to support MADV_DONTNEED for this syscall. Do we need to change these access checks again with that support?
Eh, I absolutely don't think letting another process discard memory in another process' address space is a good idea. The target process can observe that easily and might even run into real issues.
What's the use case?
Userspace oom reaper. Please look at https://lore.kernel.org/linux-api/20201014183943.GA1489464@google.com/T/
Thanks, somehow I missed that (not that it really changed my opinion on the approach while skimming over the discussion :) will have a more detailed look)
The latest version of that patchset is: https://lore.kernel.org/patchwork/patch/1344419/ Yeah, memory reaping is a special case when we are operating on a dying process to speed up the release of its memory. I don't know if for that particular case we need to make the checks stricter. It's a dying process anyway and the data is being destroyed. Allowing to speed up that process probably can still use CAP_SYS_NICE.
I know, unrelated discussion (sorry, I don't have above thread in my archive anymore due to automatic cleanups ...) , but introducing MADV_DONTEED on a remote processes, having to tweak range logic because we always want to apply it to the whole MM, just to speed up memory reaping sounds like completely abusing madvise()/process_madvise() to me.
You want different semantics than MADV_DONTNEED. You want different semantics than madvise.
Simple example: mlock()ed pages in the target process. MADV_DONTNEED would choke on that. For the use case of reaping, you certainly don't care.
I am not sure if process_madvise() is the right interface to enforce discarding of all target memory.
Not to mention that MADV_FREE doesn't make any sense IMHO for memory reaping ... no to mention exposing this via process_madvise().
On Fri, Mar 5, 2021 at 10:23 AM David Hildenbrand david@redhat.com wrote:
On 05.03.21 19:08, Suren Baghdasaryan wrote:
On Fri, Mar 5, 2021 at 9:52 AM David Hildenbrand david@redhat.com wrote:
On 05.03.21 18:45, Shakeel Butt wrote:
On Fri, Mar 5, 2021 at 9:37 AM David Hildenbrand david@redhat.com wrote:
On 04.03.21 01:03, Shakeel Butt wrote:
On Wed, Mar 3, 2021 at 3:34 PM Suren Baghdasaryan surenb@google.com wrote: > > On Wed, Mar 3, 2021 at 3:17 PM Shakeel Butt shakeelb@google.com wrote: >> >> On Wed, Mar 3, 2021 at 10:58 AM Suren Baghdasaryan surenb@google.com wrote: >>> >>> process_madvise currently requires ptrace attach capability. >>> PTRACE_MODE_ATTACH gives one process complete control over another >>> process. It effectively removes the security boundary between the >>> two processes (in one direction). Granting ptrace attach capability >>> even to a system process is considered dangerous since it creates an >>> attack surface. This severely limits the usage of this API. >>> The operations process_madvise can perform do not affect the correctness >>> of the operation of the target process; they only affect where the data >>> is physically located (and therefore, how fast it can be accessed). >>> What we want is the ability for one process to influence another process >>> in order to optimize performance across the entire system while leaving >>> the security boundary intact. >>> Replace PTRACE_MODE_ATTACH with a combination of PTRACE_MODE_READ >>> and CAP_SYS_NICE. PTRACE_MODE_READ to prevent leaking ASLR metadata >>> and CAP_SYS_NICE for influencing process performance. >>> >>> Cc: stable@vger.kernel.org # 5.10+ >>> Signed-off-by: Suren Baghdasaryan surenb@google.com >>> Reviewed-by: Kees Cook keescook@chromium.org >>> Acked-by: Minchan Kim minchan@kernel.org >>> Acked-by: David Rientjes rientjes@google.com >>> --- >>> changes in v3 >>> - Added Reviewed-by: Kees Cook keescook@chromium.org >>> - Created man page for process_madvise per Andrew's request: https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/commit/?id=a144f... >>> - cc'ed stable@vger.kernel.org # 5.10+ per Andrew's request >>> - cc'ed linux-security-module@vger.kernel.org per James Morris's request >>> >>> mm/madvise.c | 13 ++++++++++++- >>> 1 file changed, 12 insertions(+), 1 deletion(-) >>> >>> diff --git a/mm/madvise.c b/mm/madvise.c >>> index df692d2e35d4..01fef79ac761 100644 >>> --- a/mm/madvise.c >>> +++ b/mm/madvise.c >>> @@ -1198,12 +1198,22 @@ SYSCALL_DEFINE5(process_madvise, int, pidfd, const struct iovec __user *, vec, >>> goto release_task; >>> } >>> >>> - mm = mm_access(task, PTRACE_MODE_ATTACH_FSCREDS); >>> + /* Require PTRACE_MODE_READ to avoid leaking ASLR metadata. */ >>> + mm = mm_access(task, PTRACE_MODE_READ_FSCREDS); >>> if (IS_ERR_OR_NULL(mm)) { >>> ret = IS_ERR(mm) ? PTR_ERR(mm) : -ESRCH; >>> goto release_task; >>> } >>> >>> + /* >>> + * Require CAP_SYS_NICE for influencing process performance. Note that >>> + * only non-destructive hints are currently supported. >> >> How is non-destructive defined? Is MADV_DONTNEED non-destructive? > > Non-destructive in this context means the data is not lost and can be > recovered. I follow the logic described in > https://lwn.net/Articles/794704/ where Minchan was introducing > MADV_COLD and MADV_PAGEOUT as non-destructive versions of MADV_FREE > and MADV_DONTNEED. Following that logic, MADV_FREE and MADV_DONTNEED > would be considered destructive hints. > Note that process_madvise_behavior_valid() allows only MADV_COLD and > MADV_PAGEOUT at the moment, which are both non-destructive. >
There is a plan to support MADV_DONTNEED for this syscall. Do we need to change these access checks again with that support?
Eh, I absolutely don't think letting another process discard memory in another process' address space is a good idea. The target process can observe that easily and might even run into real issues.
What's the use case?
Userspace oom reaper. Please look at https://lore.kernel.org/linux-api/20201014183943.GA1489464@google.com/T/
Thanks, somehow I missed that (not that it really changed my opinion on the approach while skimming over the discussion :) will have a more detailed look)
The latest version of that patchset is: https://lore.kernel.org/patchwork/patch/1344419/ Yeah, memory reaping is a special case when we are operating on a dying process to speed up the release of its memory. I don't know if for that particular case we need to make the checks stricter. It's a dying process anyway and the data is being destroyed. Allowing to speed up that process probably can still use CAP_SYS_NICE.
I know, unrelated discussion (sorry, I don't have above thread in my archive anymore due to automatic cleanups ...) , but introducing MADV_DONTEED on a remote processes, having to tweak range logic because we always want to apply it to the whole MM, just to speed up memory reaping sounds like completely abusing madvise()/process_madvise() to me.
You want different semantics than MADV_DONTNEED. You want different semantics than madvise.
Simple example: mlock()ed pages in the target process. MADV_DONTNEED would choke on that. For the use case of reaping, you certainly don't care.
I am not sure if process_madvise() is the right interface to enforce discarding of all target memory.
Not to mention that MADV_FREE doesn't make any sense IMHO for memory reaping ... no to mention exposing this via process_madvise().
Yeah, that was the last comment from Christoph Hellwig on https://lore.kernel.org/patchwork/patch/1344418/ I'll be rethinking the whole approach. Previously I proposed couple different approaches that would make reaping a part of the kill by adding a new flag for pidfd_send_signal: https://lore.kernel.org/patchwork/patch/1338196/ https://lore.kernel.org/patchwork/patch/1060407/ but maybe a separate syscall for reaping is indeed the right way to go...
-- Thanks,
David / dhildenb
Am 05.03.2021 um 19:36 schrieb Suren Baghdasaryan surenb@google.com:
On Fri, Mar 5, 2021 at 10:23 AM David Hildenbrand david@redhat.com wrote:
On 05.03.21 19:08, Suren Baghdasaryan wrote: On Fri, Mar 5, 2021 at 9:52 AM David Hildenbrand david@redhat.com wrote:
On 05.03.21 18:45, Shakeel Butt wrote:
On Fri, Mar 5, 2021 at 9:37 AM David Hildenbrand david@redhat.com wrote:
On 04.03.21 01:03, Shakeel Butt wrote: > On Wed, Mar 3, 2021 at 3:34 PM Suren Baghdasaryan surenb@google.com wrote: >> >> On Wed, Mar 3, 2021 at 3:17 PM Shakeel Butt shakeelb@google.com wrote: >>> >>> On Wed, Mar 3, 2021 at 10:58 AM Suren Baghdasaryan surenb@google.com wrote: >>>> >>>> process_madvise currently requires ptrace attach capability. >>>> PTRACE_MODE_ATTACH gives one process complete control over another >>>> process. It effectively removes the security boundary between the >>>> two processes (in one direction). Granting ptrace attach capability >>>> even to a system process is considered dangerous since it creates an >>>> attack surface. This severely limits the usage of this API. >>>> The operations process_madvise can perform do not affect the correctness >>>> of the operation of the target process; they only affect where the data >>>> is physically located (and therefore, how fast it can be accessed). >>>> What we want is the ability for one process to influence another process >>>> in order to optimize performance across the entire system while leaving >>>> the security boundary intact. >>>> Replace PTRACE_MODE_ATTACH with a combination of PTRACE_MODE_READ >>>> and CAP_SYS_NICE. PTRACE_MODE_READ to prevent leaking ASLR metadata >>>> and CAP_SYS_NICE for influencing process performance. >>>> >>>> Cc: stable@vger.kernel.org # 5.10+ >>>> Signed-off-by: Suren Baghdasaryan surenb@google.com >>>> Reviewed-by: Kees Cook keescook@chromium.org >>>> Acked-by: Minchan Kim minchan@kernel.org >>>> Acked-by: David Rientjes rientjes@google.com >>>> --- >>>> changes in v3 >>>> - Added Reviewed-by: Kees Cook keescook@chromium.org >>>> - Created man page for process_madvise per Andrew's request: https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/commit/?id=a144f... >>>> - cc'ed stable@vger.kernel.org # 5.10+ per Andrew's request >>>> - cc'ed linux-security-module@vger.kernel.org per James Morris's request >>>> >>>> mm/madvise.c | 13 ++++++++++++- >>>> 1 file changed, 12 insertions(+), 1 deletion(-) >>>> >>>> diff --git a/mm/madvise.c b/mm/madvise.c >>>> index df692d2e35d4..01fef79ac761 100644 >>>> --- a/mm/madvise.c >>>> +++ b/mm/madvise.c >>>> @@ -1198,12 +1198,22 @@ SYSCALL_DEFINE5(process_madvise, int, pidfd, const struct iovec __user *, vec, >>>> goto release_task; >>>> } >>>> >>>> - mm = mm_access(task, PTRACE_MODE_ATTACH_FSCREDS); >>>> + /* Require PTRACE_MODE_READ to avoid leaking ASLR metadata. */ >>>> + mm = mm_access(task, PTRACE_MODE_READ_FSCREDS); >>>> if (IS_ERR_OR_NULL(mm)) { >>>> ret = IS_ERR(mm) ? PTR_ERR(mm) : -ESRCH; >>>> goto release_task; >>>> } >>>> >>>> + /* >>>> + * Require CAP_SYS_NICE for influencing process performance. Note that >>>> + * only non-destructive hints are currently supported. >>> >>> How is non-destructive defined? Is MADV_DONTNEED non-destructive? >> >> Non-destructive in this context means the data is not lost and can be >> recovered. I follow the logic described in >> https://lwn.net/Articles/794704/ where Minchan was introducing >> MADV_COLD and MADV_PAGEOUT as non-destructive versions of MADV_FREE >> and MADV_DONTNEED. Following that logic, MADV_FREE and MADV_DONTNEED >> would be considered destructive hints. >> Note that process_madvise_behavior_valid() allows only MADV_COLD and >> MADV_PAGEOUT at the moment, which are both non-destructive. >> > > There is a plan to support MADV_DONTNEED for this syscall. Do we need > to change these access checks again with that support?
Eh, I absolutely don't think letting another process discard memory in another process' address space is a good idea. The target process can observe that easily and might even run into real issues.
What's the use case?
Userspace oom reaper. Please look at https://lore.kernel.org/linux-api/20201014183943.GA1489464@google.com/T/
Thanks, somehow I missed that (not that it really changed my opinion on the approach while skimming over the discussion :) will have a more detailed look)
The latest version of that patchset is: https://lore.kernel.org/patchwork/patch/1344419/ Yeah, memory reaping is a special case when we are operating on a dying process to speed up the release of its memory. I don't know if for that particular case we need to make the checks stricter. It's a dying process anyway and the data is being destroyed. Allowing to speed up that process probably can still use CAP_SYS_NICE.
I know, unrelated discussion (sorry, I don't have above thread in my archive anymore due to automatic cleanups ...) , but introducing MADV_DONTEED on a remote processes, having to tweak range logic because we always want to apply it to the whole MM, just to speed up memory reaping sounds like completely abusing madvise()/process_madvise() to me.
You want different semantics than MADV_DONTNEED. You want different semantics than madvise.
Simple example: mlock()ed pages in the target process. MADV_DONTNEED would choke on that. For the use case of reaping, you certainly don't care.
I am not sure if process_madvise() is the right interface to enforce discarding of all target memory.
Not to mention that MADV_FREE doesn't make any sense IMHO for memory reaping ... no to mention exposing this via process_madvise().
Yeah, that was the last comment from Christoph Hellwig on https://lore.kernel.org/patchwork/patch/1344418/ I'll be rethinking the whole approach. Previously I proposed couple different approaches that would make reaping a part of the kill by adding a new flag for pidfd_send_signal: https://lore.kernel.org/patchwork/patch/1338196/ https://lore.kernel.org/patchwork/patch/1060407/ but maybe a separate syscall for reaping is indeed the right way to go...
Yeah, most likely!
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