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| author | Andy Lutomirski <luto@kernel.org> | 2015-07-15 14:25:16 -0700 |
|---|---|---|
| committer | Ingo Molnar <mingo@kernel.org> | 2015-07-17 16:08:22 +0200 |
| commit | d132803e6c611d50c19baedc8ae520203a2baca7 (patch) | |
| tree | faa0c0ae7df6e3b071f450bb0ac6eb8f8028154b /arch/x86/entry | |
| parent | 8f7f06b87acd2e017d6c536f59e10045dd8d0578 (diff) | |
| download | linux-d132803e6c611d50c19baedc8ae520203a2baca7.tar.gz linux-d132803e6c611d50c19baedc8ae520203a2baca7.tar.bz2 linux-d132803e6c611d50c19baedc8ae520203a2baca7.zip | |
x86/entry: Fix _TIF_USER_RETURN_NOTIFY check in prepare_exit_to_usermode
Linus noticed that the early return check was missing
_TIF_USER_RETURN_NOTIFY. If the only work flag was
_TIF_USER_RETURN_NOTIFY, we'd skip user return notifiers. Fix
it. (This is the only missing bit.)
This fixes double faults on a KVM host. It's the same issue as
last time, except that this time it's very easy to trigger.
Apparently no one uses -next as a KVM host.
( I'm still not quite sure what it is that KVM does that blows up
so badly if we miss a user return notifier. My best guess is that KVM
lets KERNEL_GS_BASE (i.e. the user's gs base) be negative and fixes
it up in a user return notifier. If we actually end up in user mode
with a negative gs base, we blow up pretty badly. )
Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Andy Lutomirski <luto@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Fixes: c5c46f59e4e7 ("x86/entry: Add new, comprehensible entry and exit handlers written in C")
Link: http://lkml.kernel.org/r/3f801104d24ee7a6bb1446408d9950777aa63277.1436995419.git.luto@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'arch/x86/entry')
| -rw-r--r-- | arch/x86/entry/common.c | 3 |
1 files changed, 2 insertions, 1 deletions
diff --git a/arch/x86/entry/common.c b/arch/x86/entry/common.c index febc53086a69..a3e9c7fa15d9 100644 --- a/arch/x86/entry/common.c +++ b/arch/x86/entry/common.c @@ -264,7 +264,8 @@ __visible void prepare_exit_to_usermode(struct pt_regs *regs) READ_ONCE(pt_regs_to_thread_info(regs)->flags); if (!(cached_flags & (_TIF_SIGPENDING | _TIF_NOTIFY_RESUME | - _TIF_UPROBE | _TIF_NEED_RESCHED))) + _TIF_UPROBE | _TIF_NEED_RESCHED | + _TIF_USER_RETURN_NOTIFY))) break; /* We have work to do. */ |