From: Dave Martin Date: Fri, 18 Aug 2017 15:57:01 +0000 (+0100) Subject: arm64: fpsimd: Prevent registers leaking across exec X-Git-Tag: v4.14-rc1~250^2~3 X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=096622104e14d8a1db4860bd557717067a0515d2;p=platform%2Fkernel%2Flinux-rpi3.git arm64: fpsimd: Prevent registers leaking across exec 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@vger.kernel.org Fixes: 674c242c9323 ("arm64: flush FP/SIMD state correctly after execve()") Reviewed-by: Ard Biesheuvel Signed-off-by: Dave Martin Signed-off-by: Will Deacon --- diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c index 06da8ea..c7b4995 100644 --- a/arch/arm64/kernel/fpsimd.c +++ b/arch/arm64/kernel/fpsimd.c @@ -161,9 +161,11 @@ void fpsimd_flush_thread(void) { if (!system_supports_fpsimd()) return; + 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(); } /*