Re: [patch V2 13/52] x86/fpu: Clean up fpregs_set()

Borislav Petkov
2021-06-16T15:44:54Z

On Mon, Jun 14, 2021 at 05:44:21PM +0200, Thomas Gleixner wrote:
> From: Andy Lutomirski <luto@kernel.org>
>
> fpregs_set() had unnecessary complexity to support short or nonzero-offset
> writes and to handle the case in which a copy from userspace overwrites
> some of the target buffer and then fails. Support for partial writes is
> useless -- just require that the write have offset 0 and the correct size,
> and copy into a temporary kernel buffer to avoid clobbering the state if
> the user access fails.
>
> Signed-off-by: Andy Lutomirski <luto@kernel.org>
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> ---
> V2: New patch. Picked up from Andy
> ---
> arch/x86/kernel/fpu/regset.c | 27 ++++++++++++++-------------
> 1 file changed, 14 insertions(+), 13 deletions(-)
> ---
> --- a/arch/x86/kernel/fpu/regset.c
> +++ b/arch/x86/kernel/fpu/regset.c
> @@ -305,31 +305,32 @@ int fpregs_set(struct task_struct *targe
> struct user_i387_ia32_struct env;
> int ret;
>
> - fpu__prepare_write(fpu);
> - fpstate_sanitize_xstate(fpu);
> + /* No funny business with partial or oversized writes is permitted. */
> + if (pos != 0 || count != sizeof(struct user_i387_ia32_struct))
> + return -EINVAL;
>
> if (!boot_cpu_has(X86_FEATURE_FPU))

cpu_feature_enabled(), and below too, while you're at it.

> return fpregs_soft_set(target, regset, pos, count, kbuf, ubuf);
>
> - if (!boot_cpu_has(X86_FEATURE_FXSR))
> - return user_regset_copyin(&pos, &count, &kbuf, &ubuf,
> - &fpu->state.fsave, 0,
> - -1);
> + ret = user_regset_copyin(&pos, &count, &kbuf, &ubuf, &env, 0, -1);
> + if (ret)
> + return ret;
>
> - if (pos > 0 || count < sizeof(env))
> - convert_from_fxsr(&env, target);
> + fpu__prepare_write(fpu);
>
> - ret = user_regset_copyin(&pos, &count, &kbuf, &ubuf, &env, 0, -1);
> - if (!ret)
> + if (static_cpu_has(X86_FEATURE_FXSR))
> convert_to_fxsr(&target->thread.fpu.state.fxsave, &env);
> + else
> + memcpy(&target->thread.fpu.state.fsave, &env, sizeof(env));
>
> /*
> - * update the header bit in the xsave header, indicating the
> + * Update the header bit in the xsave header, indicating the
> * presence of FP.
> */
> - if (boot_cpu_has(X86_FEATURE_XSAVE))
> + if (static_cpu_has(X86_FEATURE_XSAVE))
> fpu->state.xsave.header.xfeatures |= XFEATURE_MASK_FP;
> - return ret;
> +
> + return 0;
> }

With that addressed:

Reviewed-by: Borislav Petkov <bp@suse.de>

Thx.

--
Regards/Gruss,
Boris.

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