diff options
| author | Suresh Siddha <suresh.b.siddha@intel.com> | 2009-04-09 15:24:34 -0700 |
|---|---|---|
| committer | H. Peter Anvin <hpa@linux.intel.com> | 2009-04-20 14:33:00 -0700 |
| commit | 06c38d5e36b12d040839ff224e805146c0368556 (patch) | |
| tree | 3f4cbb95319fd7b113cb1b88df7c5ee2d416a948 | |
| parent | fc61e6636d13eb3a23eb29b4327eeee9de0ef3bc (diff) | |
x86-64: fix FPU corruption with signals and preemption
In 64bit signal delivery path, clear_used_math() was happening before saving
the current active FPU state on to the user stack for signal handling. Between
clear_used_math() and the state store on to the user stack, potentially we
can get a page fault for the user address and can block. Infact, while testing
we were hitting the might_fault() in __clear_user() which can do a schedule().
At a later point in time, we will schedule back into this process and
resume the save state (using "xsave/fxsave" instruction) which can lead
to DNA fault. And as used_math was cleared before, we will reinit the FP state
in the DNA fault and continue. This reinit will result in loosing the
FPU state of the process.
Move clear_used_math() to a point after the FPU state has been stored
onto the user stack.
This issue is present from a long time (even before the xsave changes
and the x86 merge). But it can easily be exposed in 2.6.28.x and 2.6.29.x
series because of the __clear_user() in this path, which has an explicit
__cond_resched() leading to a context switch with CONFIG_PREEMPT_VOLUNTARY.
[ Impact: fix FPU state corruption ]
Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
Cc: <stable@kernel.org> [2.6.28.x, 2.6.29.x]
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
| -rw-r--r-- | arch/x86/kernel/xsave.c | 4 |
1 files changed, 3 insertions, 1 deletions
diff --git a/arch/x86/kernel/xsave.c b/arch/x86/kernel/xsave.c index 0a5b04aa98f1..c5ee17e8c6d9 100644 --- a/arch/x86/kernel/xsave.c +++ b/arch/x86/kernel/xsave.c @@ -89,7 +89,7 @@ int save_i387_xstate(void __user *buf) if (!used_math()) return 0; - clear_used_math(); /* trigger finit */ + if (task_thread_info(tsk)->status & TS_USEDFPU) { /* * Start with clearing the user buffer. This will present a @@ -114,6 +114,8 @@ int save_i387_xstate(void __user *buf) return -1; } + clear_used_math(); /* trigger finit */ + if (task_thread_info(tsk)->status & TS_XSAVE) { struct _fpstate __user *fx = buf; struct _xstate __user *x = buf; |