diff options
| author | Kyle Huey <me@kylehuey.com> | 2022-11-15 15:09:31 -0800 |
|---|---|---|
| committer | Dave Hansen <dave.hansen@linux.intel.com> | 2022-11-16 15:06:34 -0800 |
| commit | d7e5aceace514a2b1b3ca3dc44f93f1704766ca7 (patch) | |
| tree | 08386bed10446392de558db795c658990c5a03ed /arch/x86/kernel/fpu/core.c | |
| parent | 4a804c4f8356393d6b5eff7600f07615d7869c13 (diff) | |
x86/fpu: Emulate XRSTOR's behavior if the xfeatures PKRU bit is not set
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: e84ba47e313d ("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
Diffstat (limited to 'arch/x86/kernel/fpu/core.c')
| -rw-r--r-- | arch/x86/kernel/fpu/core.c | 8 |
1 files changed, 8 insertions, 0 deletions
diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c index 46b935bc87c8..8d0f6019c21d 100644 --- a/arch/x86/kernel/fpu/core.c +++ b/arch/x86/kernel/fpu/core.c @@ -404,6 +404,14 @@ int fpu_copy_uabi_to_guest_fpstate(struct fpu_guest *gfpu, const void *buf, if (ustate->xsave.header.xfeatures & ~xcr0) return -EINVAL; + /* + * Nullify @vpkru to preserve its current value if PKRU's bit isn't set + * in the header. KVM's odd ABI is to leave PKRU untouched in this + * case (all other components are eventually re-initialized). + */ + if (!(ustate->xsave.header.xfeatures & XFEATURE_MASK_PKRU)) + vpkru = NULL; + return copy_uabi_from_kernel_to_xstate(kstate, ustate, vpkru); } EXPORT_SYMBOL_GPL(fpu_copy_uabi_to_guest_fpstate); |