Re: [PATCH 16/22] x86/fpu: Always store the registers in copy_fpstate_to_sigframe()

Borislav Petkov
2019-01-30T11:43:22Z

On Wed, Jan 09, 2019 at 12:47:38PM +0100, Sebastian Andrzej Siewior wrote:
> From: Rik van Riel <riel@surriel.com>
>
> copy_fpstate_to_sigframe() stores the registers directly to user space.
> This is okay because the FPU register are valid and saving it directly
> avoids saving it into kernel memory and making a copy.
> However… We can't keep doing this if we are going to restore the FPU
> registers on the return to userland. It is possible that the FPU
> registers will be invalidated in the middle of the save operation and
> this should be done with disabled preemption / BH.
>
> Save the FPU registers to task's FPU struct and copy them to the user
> memory later on.
>
> This code is extracted from an earlier version of the patchset while
> there still was lazy-FPU on x86.
>
> Signed-off-by: Rik van Riel <riel@surriel.com>
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> ---
> arch/x86/include/asm/fpu/internal.h | 45 -----------------------------
> arch/x86/kernel/fpu/signal.c | 29 +++++++------------
> 2 files changed, 10 insertions(+), 64 deletions(-)

...

> @@ -171,9 +156,15 @@ int copy_fpstate_to_sigframe(void __user *buf, void __user *buf_fx, int size)
> sizeof(struct user_i387_ia32_struct), NULL,
> (struct _fpstate_32 __user *) buf) ? -1 : 1;
>
> - /* Save the live register state to the user directly. */
> - if (copy_fpregs_to_sigframe(buf_fx))
> - return -1;
> + copy_fpregs_to_fpstate(fpu);
> +
> + if (using_compacted_format()) {
> + copy_xstate_to_user(buf_fx, xsave, 0, size);
> + } else {
> + fpstate_sanitize_xstate(fpu);
> + if (__copy_to_user(buf_fx, xsave, fpu_user_xstate_size))
> + return -1;
> + }
>
> /* Save the fsave header for the 32-bit frames. */
> if ((ia32_fxstate || !use_fxsr()) && save_fsave_header(tsk, buf))

Comments above that function need updating.

--
Regards/Gruss,
Boris.

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