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Commit 4a804c4f authored by Kyle Huey's avatar Kyle Huey Committed by Dave Hansen
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x86/fpu: Allow PKRU to be (once again) written by ptrace.



Move KVM's PKRU handling code in fpu_copy_uabi_to_guest_fpstate() to
copy_uabi_to_xstate() so that it is shared with other APIs that write the
XSTATE such as PTRACE_SETREGSET with NT_X86_XSTATE.

This restores the pre-5.14 behavior of ptrace. The regression can be seen
by running gdb and executing `p $pkru`, `set $pkru = 42`, and `p $pkru`.
On affected kernels (5.14+) the write to the PKRU register (which gdb
performs through ptrace) is ignored.

[ dhansen: removed stable@ tag for now.  The ABI was broken for long
	   enough that this is not urgent material.  Let's let it stew
	   in tip for a few weeks before it's submitted to stable
	   because there are so many ABIs potentially affected. ]

Fixes: e84ba47e ("x86/fpu: Hook up PKRU into ptrace()")
Signed-off-by: default avatarKyle Huey <me@kylehuey.com>
Signed-off-by: default avatarDave Hansen <dave.hansen@linux.intel.com>
Link: https://lore.kernel.org/all/20221115230932.7126-5-khuey%40kylehuey.com
parent 2c87767c
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