[PATCH 06/14] x86/ptrace: run seccomp after ptrace

Kees Cook keescook at chromium.org
Fri Jun 10 07:01:56 AEST 2016


This moves seccomp after ptrace on x86 to that seccomp can catch changes
made by ptrace. Emulation should skip the rest of processing too.

We can get rid of test_thread_flag because there's no longer any
opportunity for seccomp to mess with ptrace state before invoking
ptrace.

Suggested-by: Andy Lutomirski <luto at kernel.org>
Signed-off-by: Kees Cook <keescook at chromium.org>
Cc: x86 at kernel.org
Cc: Andy Lutomirski <luto at kernel.org>
---
 arch/x86/entry/common.c | 22 ++++++++++++----------
 1 file changed, 12 insertions(+), 10 deletions(-)

diff --git a/arch/x86/entry/common.c b/arch/x86/entry/common.c
index df56ca394877..81c0e12d831c 100644
--- a/arch/x86/entry/common.c
+++ b/arch/x86/entry/common.c
@@ -73,6 +73,7 @@ static long syscall_trace_enter(struct pt_regs *regs)
 
 	struct thread_info *ti = pt_regs_to_thread_info(regs);
 	unsigned long ret = 0;
+	bool emulated = false;
 	u32 work;
 
 	if (IS_ENABLED(CONFIG_DEBUG_ENTRY))
@@ -80,11 +81,19 @@ static long syscall_trace_enter(struct pt_regs *regs)
 
 	work = ACCESS_ONCE(ti->flags) & _TIF_WORK_SYSCALL_ENTRY;
 
+	if (unlikely(work & _TIF_SYSCALL_EMU))
+		emulated = true;
+
+	if ((emulated || (work & _TIF_SYSCALL_TRACE)) &&
+	    tracehook_report_syscall_entry(regs))
+		return -1L;
+
+	if (emulated)
+		return -1L;
+
 #ifdef CONFIG_SECCOMP
 	/*
-	 * Do seccomp first -- it should minimize exposure of other
-	 * code, and keeping seccomp fast is probably more valuable
-	 * than the rest of this.
+	 * Do seccomp after ptrace, to catch any tracer changes.
 	 */
 	if (work & _TIF_SECCOMP) {
 		struct seccomp_data sd;
@@ -117,13 +126,6 @@ static long syscall_trace_enter(struct pt_regs *regs)
 	}
 #endif
 
-	if (unlikely(work & _TIF_SYSCALL_EMU))
-		ret = -1L;
-
-	if ((ret || test_thread_flag(TIF_SYSCALL_TRACE)) &&
-	    tracehook_report_syscall_entry(regs))
-		ret = -1L;
-
 	if (unlikely(test_thread_flag(TIF_SYSCALL_TRACEPOINT)))
 		trace_sys_enter(regs, regs->orig_ax);
 
-- 
2.7.4



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