Messages in this thread | | | Date | Wed, 17 Jun 2020 10:33:14 +0200 | From | Borislav Petkov <> | Subject | Re: [PATCH] x86/fpu: Reset MXCSR to default in kernel_fpu_begin() |
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On Tue, Jun 16, 2020 at 02:17:16PM -0700, Andy Lutomirski wrote: > We definitely need to sanitize MXCSR for kernel fpu if kernel fpu > means SSE2. If kernel fpu means x87, we need to fix the fpu control > word.
Bah, there's no need to beat around the bush - let's just do:
if (boot_cpu_has(X86_FEATURE_XMM)) ldmxcsr(MXCSR_DEFAULT);
if (boot_cpu_has(X86_FEATURE_FPU)) asm volatile ("fninit");
and be sure that kernel users get a squeaky-clean FPU.
> On x86_64, I suspect the UEFI ABI technically requires a clean x87 > control word too. If we’re willing to declare that the kernel proper > won’t use x87, then we could shove that into the UEFI code.
Nah, we don't trust the firmware.
-- Regards/Gruss, Boris.
https://people.kernel.org/tglx/notes-about-netiquette
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