diff mbox

ARM: ptrace: reload syscall number after secure_computing() check

Message ID 1403600096-26088-1-git-send-email-will.deacon@arm.com
State Accepted
Commit 42309ab450b608ddcfafa90e4cfa93a5001ecfba
Headers show

Commit Message

Will Deacon June 24, 2014, 8:54 a.m. UTC 
On the syscall tracing path, we call out to secure_computing() to allow
seccomp to check the syscall number being attempted. As part of this, a
SIGTRAP may be sent to the tracer and the syscall could be re-written by
a subsequent SET_SYSCALL ptrace request. Unfortunately, this new syscall
is ignored by the current code unless TIF_SYSCALL_TRACE is also set on
the current thread.

This patch slightly reworks the enter path of the syscall tracing code
so that we always reload the syscall number from
current_thread_info()->syscall after the potential ptrace traps.

Tested-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>
---
 arch/arm/kernel/ptrace.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

Comments

Kees Cook June 24, 2014, 2:18 p.m. UTC | #1 
On Tue, Jun 24, 2014 at 1:54 AM, Will Deacon <will.deacon@arm.com> wrote:
> On the syscall tracing path, we call out to secure_computing() to allow
> seccomp to check the syscall number being attempted. As part of this, a
> SIGTRAP may be sent to the tracer and the syscall could be re-written by
> a subsequent SET_SYSCALL ptrace request. Unfortunately, this new syscall
> is ignored by the current code unless TIF_SYSCALL_TRACE is also set on
> the current thread.
>
> This patch slightly reworks the enter path of the syscall tracing code
> so that we always reload the syscall number from
> current_thread_info()->syscall after the potential ptrace traps.
>
> Tested-by: Kees Cook <keescook@chromium.org>
> Signed-off-by: Will Deacon <will.deacon@arm.com>

Acked-by: Kees Cook <keescook@chromium.org>

Thanks!

-Kees

> ---
>  arch/arm/kernel/ptrace.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/arch/arm/kernel/ptrace.c b/arch/arm/kernel/ptrace.c
> index 0dd3b79b15c3..0c27ed6f3f23 100644
> --- a/arch/arm/kernel/ptrace.c
> +++ b/arch/arm/kernel/ptrace.c
> @@ -908,7 +908,7 @@ enum ptrace_syscall_dir {
>         PTRACE_SYSCALL_EXIT,
>  };
>
> -static int tracehook_report_syscall(struct pt_regs *regs,
> +static void tracehook_report_syscall(struct pt_regs *regs,
>                                     enum ptrace_syscall_dir dir)
>  {
>         unsigned long ip;
> @@ -926,7 +926,6 @@ static int tracehook_report_syscall(struct pt_regs *regs,
>                 current_thread_info()->syscall = -1;
>
>         regs->ARM_ip = ip;
> -       return current_thread_info()->syscall;
>  }
>
>  asmlinkage int syscall_trace_enter(struct pt_regs *regs, int scno)
> @@ -938,7 +937,9 @@ asmlinkage int syscall_trace_enter(struct pt_regs *regs, int scno)
>                 return -1;
>
>         if (test_thread_flag(TIF_SYSCALL_TRACE))
> -               scno = tracehook_report_syscall(regs, PTRACE_SYSCALL_ENTER);
> +               tracehook_report_syscall(regs, PTRACE_SYSCALL_ENTER);
> +
> +       scno = current_thread_info()->syscall;
>
>         if (test_thread_flag(TIF_SYSCALL_TRACEPOINT))
>                 trace_sys_enter(regs, scno);
> --
> 2.0.0
>
diff mbox

Patch

diff --git a/arch/arm/kernel/ptrace.c b/arch/arm/kernel/ptrace.c
index 0dd3b79b15c3..0c27ed6f3f23 100644
--- a/arch/arm/kernel/ptrace.c
+++ b/arch/arm/kernel/ptrace.c
@@ -908,7 +908,7 @@  enum ptrace_syscall_dir {
 	PTRACE_SYSCALL_EXIT,
 };
 
-static int tracehook_report_syscall(struct pt_regs *regs,
+static void tracehook_report_syscall(struct pt_regs *regs,
 				    enum ptrace_syscall_dir dir)
 {
 	unsigned long ip;
@@ -926,7 +926,6 @@  static int tracehook_report_syscall(struct pt_regs *regs,
 		current_thread_info()->syscall = -1;
 
 	regs->ARM_ip = ip;
-	return current_thread_info()->syscall;
 }
 
 asmlinkage int syscall_trace_enter(struct pt_regs *regs, int scno)
@@ -938,7 +937,9 @@  asmlinkage int syscall_trace_enter(struct pt_regs *regs, int scno)
 		return -1;
 
 	if (test_thread_flag(TIF_SYSCALL_TRACE))
-		scno = tracehook_report_syscall(regs, PTRACE_SYSCALL_ENTER);
+		tracehook_report_syscall(regs, PTRACE_SYSCALL_ENTER);
+
+	scno = current_thread_info()->syscall;
 
 	if (test_thread_flag(TIF_SYSCALL_TRACEPOINT))
 		trace_sys_enter(regs, scno);