On Wed, Jan 18, 2023 at 03:10:53PM -0500, Gregory Price wrote:
Adds PTRACE_O_SUSPEND_SYSCALL_USER_DISPATCH to ptrace options, and modify Syscall User Dispatch to suspend interception when enabled.
This is modeled after the SUSPEND_SECCOMP feature, which suspends SECCOMP interposition. Without doing this, software like CRIU will inject system calls into a process and be intercepted by Syscall User Dispatch, either causing a crash (due to blocked signals) or the delivery of those signals to a ptracer (not the intended behavior).
Since Syscall User Dispatch is not a privileged feature, a check for permissions is not required, however attempting to set this option when CONFIG_CHECKPOINT_RESTORE it not supported should be disallowed, as its intended use is checkpoint/resume.
Signed-off-by: Gregory Price gregory.price@memverge.com
One small nit -- see below, otherwise:
Acked-by: Peter Zijlstra (Intel) peterz@infradead.org
include/linux/ptrace.h | 2 ++ include/uapi/linux/ptrace.h | 6 +++++- kernel/entry/syscall_user_dispatch.c | 5 +++++ kernel/ptrace.c | 5 +++++ 4 files changed, 17 insertions(+), 1 deletion(-)
diff --git a/include/linux/ptrace.h b/include/linux/ptrace.h index eaaef3ffec22..461ae5c99d57 100644 --- a/include/linux/ptrace.h +++ b/include/linux/ptrace.h @@ -45,6 +45,8 @@ extern int ptrace_access_vm(struct task_struct *tsk, unsigned long addr, #define PT_EXITKILL (PTRACE_O_EXITKILL << PT_OPT_FLAG_SHIFT) #define PT_SUSPEND_SECCOMP (PTRACE_O_SUSPEND_SECCOMP << PT_OPT_FLAG_SHIFT) +#define PT_SUSPEND_SYSCALL_USER_DISPATCH \
- (PTRACE_O_SUSPEND_SYSCALL_USER_DISPATCH << PT_OPT_FLAG_SHIFT)
extern long arch_ptrace(struct task_struct *child, long request, unsigned long addr, unsigned long data); diff --git a/include/uapi/linux/ptrace.h b/include/uapi/linux/ptrace.h index 195ae64a8c87..ba9e3f19a22c 100644 --- a/include/uapi/linux/ptrace.h +++ b/include/uapi/linux/ptrace.h @@ -146,9 +146,13 @@ struct ptrace_rseq_configuration { /* eventless options */ #define PTRACE_O_EXITKILL (1 << 20) #define PTRACE_O_SUSPEND_SECCOMP (1 << 21) +#define PTRACE_O_SUSPEND_SYSCALL_USER_DISPATCH (1 << 22) #define PTRACE_O_MASK (\
- 0x000000ff | PTRACE_O_EXITKILL | PTRACE_O_SUSPEND_SECCOMP)
- 0x000000ff | \
- PTRACE_O_EXITKILL | \
- PTRACE_O_SUSPEND_SECCOMP | \
- PTRACE_O_SUSPEND_SYSCALL_USER_DISPATCH)
#include <asm/ptrace.h> diff --git a/kernel/entry/syscall_user_dispatch.c b/kernel/entry/syscall_user_dispatch.c index 0b6379adff6b..7607f4598dd8 100644 --- a/kernel/entry/syscall_user_dispatch.c +++ b/kernel/entry/syscall_user_dispatch.c @@ -8,6 +8,7 @@ #include <linux/uaccess.h> #include <linux/signal.h> #include <linux/elf.h> +#include <linux/ptrace.h> #include <linux/sched/signal.h> #include <linux/sched/task_stack.h> @@ -36,6 +37,10 @@ bool syscall_user_dispatch(struct pt_regs *regs) struct syscall_user_dispatch *sd = ¤t->syscall_dispatch; char state;
- if (IS_ENABLED(CONFIG_CHECKPOINT_RESTORE) &&
unlikely(current->ptrace & PT_SUSPEND_SYSCALL_USER_DISPATCH))
Align with the '(' pleaase.
return false;- if (likely(instruction_pointer(regs) - sd->offset < sd->len)) return false;
diff --git a/kernel/ptrace.c b/kernel/ptrace.c index 54482193e1ed..a6ad815bd4be 100644 --- a/kernel/ptrace.c +++ b/kernel/ptrace.c @@ -370,6 +370,11 @@ static int check_ptrace_options(unsigned long data) if (data & ~(unsigned long)PTRACE_O_MASK) return -EINVAL;
- if (unlikely(data & PTRACE_O_SUSPEND_SYSCALL_USER_DISPATCH)) {
if (!IS_ENABLED(CONFIG_CHECKPOINT_RESTART))return -EINVAL;- }
- if (unlikely(data & PTRACE_O_SUSPEND_SECCOMP)) { if (!IS_ENABLED(CONFIG_CHECKPOINT_RESTORE) || !IS_ENABLED(CONFIG_SECCOMP))
-- 2.39.0