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


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 40361343

arch/x86/entry/common.c

+13 −10
Original line number Original line Diff line number Diff line
@@ -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) 




	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) 
	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);

}

}