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authorAndy Lutomirski <luto@kernel.org>2016-02-11 01:15:27 +0300
committerIngo Molnar <mingo@kernel.org>2016-02-17 11:51:06 +0300
commit4e79e182b419172e35936a47f098509092d69817 (patch)
tree92a43a6a378aa593e754169b520c91a91c5194e4 /arch/x86/entry/common.c
parent403613432222549727e5d70cf44da8987653202a (diff)
downloadlinux-4e79e182b419172e35936a47f098509092d69817.tar.xz
x86/entry/compat: Keep TS_COMPAT set during signal delivery
Signal delivery needs to know the sign of an interrupted syscall's return value in order to detect -ERESTART variants. Normally this works independently of bitness because syscalls internally return long. Under ptrace, however, this can break, and syscall_get_error is supposed to sign-extend regs->ax if needed. We were clearing TS_COMPAT too early, though, and this prevented sign extension, which subtly broke syscall restart under ptrace. Reported-by: Robert O'Callahan <robert@ocallahan.org> Signed-off-by: Andy Lutomirski <luto@kernel.org> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Andy Lutomirski <luto@amacapital.net> Cc: Borislav Petkov <bp@alien8.de> Cc: Brian Gerst <brgerst@gmail.com> Cc: Denys Vlasenko <dvlasenk@redhat.com> Cc: H. Peter Anvin <hpa@zytor.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Shuah Khan <shuahkh@osg.samsung.com> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: stable@vger.kernel.org # 4.3.x- Fixes: c5c46f59e4e7 ("x86/entry: Add new, comprehensible entry and exit handlers written in C") Link: http://lkml.kernel.org/r/cbce3cf545522f64eb37f5478cb59746230db3b5.1455142412.git.luto@kernel.org Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'arch/x86/entry/common.c')
-rw-r--r--arch/x86/entry/common.c23
1 files changed, 13 insertions, 10 deletions
diff --git a/arch/x86/entry/common.c b/arch/x86/entry/common.c
index c6ab2ebb5f4f..1a000f59f04a 100644
--- a/arch/x86/entry/common.c
+++ b/arch/x86/entry/common.c
@@ -269,6 +269,7 @@ static void exit_to_usermode_loop(struct pt_regs *regs, u32 cached_flags)
/* Called with IRQs disabled. */
__visible inline void prepare_exit_to_usermode(struct pt_regs *regs)
{
+ struct thread_info *ti = pt_regs_to_thread_info(regs);
u32 cached_flags;
if (IS_ENABLED(CONFIG_PROVE_LOCKING) && WARN_ON(!irqs_disabled()))
@@ -276,12 +277,22 @@ __visible inline void prepare_exit_to_usermode(struct pt_regs *regs)
lockdep_sys_exit();
- cached_flags =
- READ_ONCE(pt_regs_to_thread_info(regs)->flags);
+ cached_flags = READ_ONCE(ti->flags);
if (unlikely(cached_flags & EXIT_TO_USERMODE_LOOP_FLAGS))
exit_to_usermode_loop(regs, cached_flags);
+#ifdef CONFIG_COMPAT
+ /*
+ * Compat syscalls set TS_COMPAT. Make sure we clear it before
+ * returning to user mode. We need to clear it *after* signal
+ * handling, because syscall restart has a fixup for compat
+ * syscalls. The fixup is exercised by the ptrace_syscall_32
+ * selftest.
+ */
+ ti->status &= ~TS_COMPAT;
+#endif
+
user_enter();
}
@@ -333,14 +344,6 @@ __visible inline void syscall_return_slowpath(struct pt_regs *regs)
if (unlikely(cached_flags & SYSCALL_EXIT_WORK_FLAGS))
syscall_slow_exit_work(regs, cached_flags);
-#ifdef CONFIG_COMPAT
- /*
- * Compat syscalls set TS_COMPAT. Make sure we clear it before
- * returning to user mode.
- */
- ti->status &= ~TS_COMPAT;
-#endif
-
local_irq_disable();
prepare_exit_to_usermode(regs);
}