diff options
authorWill Deacon <will.deacon@arm.com>2012-12-07 17:34:37 +0100
committerRussell King <rmk+kernel@arm.linux.org.uk>2012-12-11 00:18:26 +0000
commitb10bca0bc699af201770989a88fa293155e9d8de (patch)
parent39b175a0092d4a8e0875c67df82285475b1da591 (diff)
ARM: 7595/1: syscall: rework ordering in syscall_trace_exit
syscall_trace_exit is currently doing things back-to-front; invoking the audit hook *after* signalling the debugger, which presents an opportunity for the registers to be re-written by userspace in order to bypass auditing constaints. This patch fixes the ordering by moving the audit code first and the tracehook code last. On the face of it, it looks like current_thread_info()->syscall may be incorrect for the sys_exit tracepoint, but that's actually not an issue because it will have been set during syscall entry and cannot have changed since then. Reported-by: Andrew Gabbasov <Andrew_Gabbasov@mentor.com> Tested-by: Mark Rutland <mark.rutland@arm.com> Signed-off-by: Will Deacon <will.deacon@arm.com> Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
2 files changed, 15 insertions, 10 deletions
diff --git a/arch/arm/kernel/entry-common.S b/arch/arm/kernel/entry-common.S
index ee81dbc6fa10..d863bbf0f1f5 100644
--- a/arch/arm/kernel/entry-common.S
+++ b/arch/arm/kernel/entry-common.S
@@ -455,7 +455,6 @@ __sys_trace:
str r0, [sp, #S_R0 + S_OFF]! @ save returned r0
- mov r1, scno
mov r0, sp
bl syscall_trace_exit
b ret_slow_syscall
diff --git a/arch/arm/kernel/ptrace.c b/arch/arm/kernel/ptrace.c
index 518536d93fba..03deeffd9f6d 100644
--- a/arch/arm/kernel/ptrace.c
+++ b/arch/arm/kernel/ptrace.c
@@ -957,17 +957,23 @@ asmlinkage int syscall_trace_enter(struct pt_regs *regs, int scno)
return scno;
-asmlinkage int syscall_trace_exit(struct pt_regs *regs, int scno)
+asmlinkage void syscall_trace_exit(struct pt_regs *regs)
- current_thread_info()->syscall = scno;
- if (test_thread_flag(TIF_SYSCALL_TRACE))
- scno = tracehook_report_syscall(regs, PTRACE_SYSCALL_EXIT);
+ /*
+ * Audit the syscall before anything else, as a debugger may
+ * come in and change the current registers.
+ */
+ audit_syscall_exit(regs);
+ /*
+ * Note that we haven't updated the ->syscall field for the
+ * current thread. This isn't a problem because it will have
+ * been set on syscall entry and there hasn't been an opportunity
+ * for a PTRACE_SET_SYSCALL since then.
+ */
if (test_thread_flag(TIF_SYSCALL_TRACEPOINT))
- trace_sys_exit(regs, scno);
- audit_syscall_exit(regs);
+ trace_sys_exit(regs, regs_return_value(regs));
- return scno;
+ if (test_thread_flag(TIF_SYSCALL_TRACE))
+ tracehook_report_syscall(regs, PTRACE_SYSCALL_EXIT);