4.15-stable review patch. If anyone has any objections, please let me know.
------------------
From: Kees Cook keescook@chromium.org
[ Upstream commit 22ec1a2aea73b9dfe340dff7945bd85af4cc6280 ]
As done for /proc/kcore in
commit df04abfd181a ("fs/proc/kcore.c: Add bounce buffer for ktext data")
this adds a bounce buffer when reading memory via /dev/mem. This is needed to allow kernel text memory to be read out when built with CONFIG_HARDENED_USERCOPY (which refuses to read out kernel text) and without CONFIG_STRICT_DEVMEM (which would have refused to read any RAM contents at all).
Since this build configuration isn't common (most systems with CONFIG_HARDENED_USERCOPY also have CONFIG_STRICT_DEVMEM), this also tries to inform Kconfig about the recommended settings.
This patch is modified from Brad Spengler/PaX Team's changes to /dev/mem code in the last public patch of grsecurity/PaX based on my understanding of the code. Changes or omissions from the original code are mine and don't reflect the original grsecurity/PaX code.
Reported-by: Michael Holzheu holzheu@linux.vnet.ibm.com Fixes: f5509cc18daa ("mm: Hardened usercopy") Signed-off-by: Kees Cook keescook@chromium.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org Signed-off-by: Sasha Levin alexander.levin@microsoft.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/char/mem.c | 27 ++++++++++++++++++++++----- security/Kconfig | 1 + 2 files changed, 23 insertions(+), 5 deletions(-)
--- a/drivers/char/mem.c +++ b/drivers/char/mem.c @@ -107,6 +107,8 @@ static ssize_t read_mem(struct file *fil phys_addr_t p = *ppos; ssize_t read, sz; void *ptr; + char *bounce; + int err;
if (p != *ppos) return 0; @@ -129,15 +131,22 @@ static ssize_t read_mem(struct file *fil } #endif
+ bounce = kmalloc(PAGE_SIZE, GFP_KERNEL); + if (!bounce) + return -ENOMEM; + while (count > 0) { unsigned long remaining; int allowed;
sz = size_inside_page(p, count);
+ err = -EPERM; allowed = page_is_allowed(p >> PAGE_SHIFT); if (!allowed) - return -EPERM; + goto failed; + + err = -EFAULT; if (allowed == 2) { /* Show zeros for restricted memory. */ remaining = clear_user(buf, sz); @@ -149,24 +158,32 @@ static ssize_t read_mem(struct file *fil */ ptr = xlate_dev_mem_ptr(p); if (!ptr) - return -EFAULT; - - remaining = copy_to_user(buf, ptr, sz); + goto failed;
+ err = probe_kernel_read(bounce, ptr, sz); unxlate_dev_mem_ptr(p, ptr); + if (err) + goto failed; + + remaining = copy_to_user(buf, bounce, sz); }
if (remaining) - return -EFAULT; + goto failed;
buf += sz; p += sz; count -= sz; read += sz; } + kfree(bounce);
*ppos += read; return read; + +failed: + kfree(bounce); + return err; }
static ssize_t write_mem(struct file *file, const char __user *buf, --- a/security/Kconfig +++ b/security/Kconfig @@ -154,6 +154,7 @@ config HARDENED_USERCOPY bool "Harden memory copies between kernel and userspace" depends on HAVE_HARDENED_USERCOPY_ALLOCATOR select BUG + imply STRICT_DEVMEM help This option checks for obviously wrong memory regions when copying memory to/from the kernel (via copy_to_user() and