x86/fpu: Emulate XRSTOR's behavior if the xfeatures PKRU bit is not set

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The hardware XRSTOR instruction resets the PKRU register to its hardware
init value (namely 0) if the PKRU bit is not set in the xfeatures mask.
Emulating that here restores the pre-5.14 behavior for PTRACE_SET_REGSET
with NT_X86_XSTATE, and makes sigreturn (which still uses XRSTOR) and
ptrace behave identically. KVM has never used XRSTOR and never had this
behavior, so KVM opts-out of this emulation by passing a NULL pkru pointer
to copy_uabi_to_xstate().

Fixes: e84ba47e31 ("x86/fpu: Hook up PKRU into ptrace()")
Signed-off-by: Kyle Huey <me@kylehuey.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Link: https://lore.kernel.org/all/20221115230932.7126-6-khuey%40kylehuey.com

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Kyle Huey 2022-11-15 15:09:31 -08:00 • committed by Dave Hansen

parent 4a804c4f83

commit d7e5aceace

2 changed files with 22 additions and 1 deletions

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8

arch/x86/kernel/fpu/core.c

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15

arch/x86/kernel/fpu/xstate.c

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