diff options
| author | Andy Lutomirski <luto@kernel.org> | 2016-02-11 01:15:27 +0300 |
|---|---|---|
| committer | Ingo Molnar <mingo@kernel.org> | 2016-02-17 11:51:06 +0300 |
| commit | 4e79e182b419172e35936a47f098509092d69817 (patch) | |
| tree | 92a43a6a378aa593e754169b520c91a91c5194e4 /arch/x86/entry/common.c | |
| parent | 403613432222549727e5d70cf44da8987653202a (diff) | |
| download | linux-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.c | 23 |
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); } |