Messages in this thread Patch in this message |  | | Date | Fri, 20 Dec 2019 20:59:06 +0100 | From | Sebastian Andrzej Siewior <> | Subject | [PATCH] x86/fpu: Deacticate FPU state after failure during state load |
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In __fpu__restore_sig() we need to reset `fpu_fpregs_owner_ctx' if the FPU state was not fully restored. Otherwise the following may happen (on the same CPU):
Task A Task B fpu_fpregs_owner_ctx *active* A.fpu __fpu__restore_sig() ctx switch load B.fpu *active* B.fpu fpregs_lock() copy_user_to_fpregs_zeroing() copy_kernel_to_xregs() *modify* copy_user_to_xregs() *fails* fpregs_unlock() ctx switch skip loading B.fpu, *active* B.fpu
In the succeess case we set `fpu_fpregs_owner_ctx' to the current task. In the failure case we *might* have modified the FPU state because we loaded the init state. In this case we need to reset `fpu_fpregs_owner_ctx' to ensure that the FPU state of the following task is loaded from saved state (and not skip because it was the previous state).
Reset `fpu_fpregs_owner_ctx' after a failure during restore occured to ensure that the FPU state for the next task is always loaded.
Fixes: 5f409e20b7945 ("x86/fpu: Defer FPU state load until return to userspace") Reported-by: Yu-cheng Yu <yu-cheng.yu@intel.com> Debugged-by: Yu-cheng Yu <yu-cheng.yu@intel.com> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> --- arch/x86/kernel/fpu/signal.c | 3 +++ 1 file changed, 3 insertions(+)
diff --git a/arch/x86/kernel/fpu/signal.c b/arch/x86/kernel/fpu/signal.c index 0071b794ed193..400a05e1c1c51 100644 --- a/arch/x86/kernel/fpu/signal.c +++ b/arch/x86/kernel/fpu/signal.c @@ -352,6 +352,7 @@ static int __fpu__restore_sig(void __user *buf, void __user *buf_fx, int size) fpregs_unlock(); return 0; } + fpregs_deactivate(fpu); fpregs_unlock(); } @@ -403,6 +404,8 @@ static int __fpu__restore_sig(void __user *buf, void __user *buf_fx, int size) } if (!ret) fpregs_mark_activate(); + else + fpregs_deactivate(fpu); fpregs_unlock(); err_out: -- 2.24.1
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