x86/entry/compat: Keep TS_COMPAT set during signal delivery (4e79e182) · Commits · 戴 / test

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: ("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>

arch/x86/entry/common.c

+13 −10

Original line number	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. */
		__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);
		}

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