From: Dave Martin <Dave.Martin@xxxxxxx>
This patch has been added to the v4.1 stable tree. If you have any
objections, please let us know.
===============
[ Upstream commit 096622104e14d8a1db4860bd557717067a0515d2 ]
There are some tricky dependencies between the different stages of
flushing the FPSIMD register state during exec, and these can race
with context switch in ways that can cause the old task's regs to
leak across. In particular, a context switch during the memset() can
cause some of the task's old FPSIMD registers to reappear.
Disabling preemption for this small window would be no big deal for
performance: preemption is already disabled for similar scenarios
like updating the FPSIMD registers in sigreturn.
So, instead of rearranging things in ways that might swap existing
subtle bugs for new ones, this patch just disables preemption
around the FPSIMD state flushing so that races of this type can't
occur here. This brings fpsimd_flush_thread() into line with other
code paths.
Cc: stable@xxxxxxxxxxxxxxx
Fixes: 674c242c9323 ("arm64: flush FP/SIMD state correctly after execve()")
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
Signed-off-by: Dave Martin <Dave.Martin@xxxxxxx>
Signed-off-by: Will Deacon <will.deacon@xxxxxxx>
Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxx>
---
arch/arm64/kernel/fpsimd.c | 2 ++
1 file changed, 2 insertions(+)
diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c
index c31e59fe2cb8..7b4e9ea0b1a4 100644
--- a/arch/arm64/kernel/fpsimd.c
+++ b/arch/arm64/kernel/fpsimd.c
@@ -156,9 +156,11 @@ void fpsimd_thread_switch(struct task_struct *next)
void fpsimd_flush_thread(void)
{
+ preempt_disable();
memset(¤t->thread.fpsimd_state, 0, sizeof(struct fpsimd_state));
fpsimd_flush_task_state(current);
set_thread_flag(TIF_FOREIGN_FPSTATE);
+ preempt_enable();
}
/*
--
2.11.0