Commit 4e79e182 authored by Andy Lutomirski's avatar Andy Lutomirski Committed by Ingo Molnar

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: default avatarRobert O'Callahan <robert@ocallahan.org>
Signed-off-by: default avatarAndy 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: c5c46f59 ("x86/entry: Add new, comprehensible entry and exit handlers written in C")
Link: http://lkml.kernel.org/r/cbce3cf545522f64eb37f5478cb59746230db3b5.1455142412.git.luto@kernel.orgSigned-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 40361343
...@@ -269,6 +269,7 @@ static void exit_to_usermode_loop(struct pt_regs *regs, u32 cached_flags) ...@@ -269,6 +269,7 @@ static void exit_to_usermode_loop(struct pt_regs *regs, u32 cached_flags)
/* Called with IRQs disabled. */ /* Called with IRQs disabled. */
__visible inline void prepare_exit_to_usermode(struct pt_regs *regs) __visible inline void prepare_exit_to_usermode(struct pt_regs *regs)
{ {
struct thread_info *ti = pt_regs_to_thread_info(regs);
u32 cached_flags; u32 cached_flags;
if (IS_ENABLED(CONFIG_PROVE_LOCKING) && WARN_ON(!irqs_disabled())) 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) ...@@ -276,12 +277,22 @@ __visible inline void prepare_exit_to_usermode(struct pt_regs *regs)
lockdep_sys_exit(); lockdep_sys_exit();
cached_flags = cached_flags = READ_ONCE(ti->flags);
READ_ONCE(pt_regs_to_thread_info(regs)->flags);
if (unlikely(cached_flags & EXIT_TO_USERMODE_LOOP_FLAGS)) if (unlikely(cached_flags & EXIT_TO_USERMODE_LOOP_FLAGS))
exit_to_usermode_loop(regs, cached_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(); user_enter();
} }
...@@ -333,14 +344,6 @@ __visible inline void syscall_return_slowpath(struct pt_regs *regs) ...@@ -333,14 +344,6 @@ __visible inline void syscall_return_slowpath(struct pt_regs *regs)
if (unlikely(cached_flags & SYSCALL_EXIT_WORK_FLAGS)) if (unlikely(cached_flags & SYSCALL_EXIT_WORK_FLAGS))
syscall_slow_exit_work(regs, cached_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(); local_irq_disable();
prepare_exit_to_usermode(regs); prepare_exit_to_usermode(regs);
} }
......
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