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x86/fpu: Allow PKRU to be (once again) written by ptrace.

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commit 4a804c4f8356393d6b5eff7600f07615d7869c13 upstream

Handle PKRU in copy_uabi_to_xstate() for the benefit of 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.

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/20221115230932.7126-5-khuey%40kylehuey.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Kyle Huey 2023-01-09 13:02:12 -08:00 committed by Greg Kroah-Hartman
parent b29773d6b0
commit 3f1c81426a
1 changed files with 30 additions and 0 deletions
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30
arch/x86/kernel/fpu/xstate.c
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@ -1091,6 +1091,29 @@ static int copy_from_buffer(void *dst, unsigned int offset, unsigned int size,
}
/**
* copy_uabi_to_xstate - Copy a UABI format buffer to the kernel xstate
* @fpstate: The fpstate buffer to copy to
* @kbuf: The UABI format buffer, if it comes from the kernel
* @ubuf: The UABI format buffer, if it comes from userspace
* @pkru: The location to write the PKRU value to
*
* Converts from the UABI format into the kernel internal hardware
* dependent format.
*
* This function ultimately has two different callers with distinct PKRU
* behavior.
* 1. When called from sigreturn the PKRU register will be restored from
* @fpstate via an XRSTOR. Correctly copying the UABI format buffer to
* @fpstate is sufficient to cover this case, but the caller will also
* pass a pointer to the thread_struct's pkru field in @pkru and updating
* it is harmless.
* 2. When called from ptrace the PKRU register will be restored from the
* thread_struct's pkru field. A pointer to that is passed in @pkru.
* The kernel will restore it manually, so the XRSTOR behavior that resets
* the PKRU register to the hardware init value (0) if the corresponding
* xfeatures bit is not set is emulated here.
*/
static int copy_uabi_to_xstate(struct xregs_state *xsave, const void *kbuf,
const void __user *ubuf, u32 *pkru)
{
@ -1140,6 +1163,13 @@ static int copy_uabi_to_xstate(struct xregs_state *xsave, const void *kbuf,
}
}
if (hdr.xfeatures & XFEATURE_MASK_PKRU) {
struct pkru_state *xpkru;
xpkru = __raw_xsave_addr(xsave, XFEATURE_PKRU);
*pkru = xpkru->pkru;
}
/*
* The state that came in from userspace was user-state only.
* Mask all the user states out of 'xfeatures':