From: Kyle Huey <me@xxxxxxxxxxxx>
commit 4a804c4f8356393d6b5eff7600f07615d7869c13 upstream.
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: e84ba47e313d ("x86/fpu: Hook up PKRU into ptrace()")
Signed-off-by: Kyle Huey <me@xxxxxxxxxxxx>
Signed-off-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Link: https://lore.kernel.org/all/20221115230932.7126-5-khuey%40kylehuey.com
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/x86/kernel/fpu/core.c | 13 +------------
arch/x86/kernel/fpu/xstate.c | 21 ++++++++++++++++++++-
2 files changed, 21 insertions(+), 13 deletions(-)
--- a/arch/x86/kernel/fpu/core.c
+++ b/arch/x86/kernel/fpu/core.c
@@ -391,8 +391,6 @@ int fpu_copy_uabi_to_guest_fpstate(struc
{
struct fpstate *kstate = gfpu->fpstate;
const union fpregs_state *ustate = buf;
- struct pkru_state *xpkru;
- int ret;
if (!cpu_feature_enabled(X86_FEATURE_XSAVE)) {
if (ustate->xsave.header.xfeatures & ~XFEATURE_MASK_FPSSE)
@@ -406,16 +404,7 @@ int fpu_copy_uabi_to_guest_fpstate(struc
if (ustate->xsave.header.xfeatures & ~xcr0)
return -EINVAL;
- ret = copy_uabi_from_kernel_to_xstate(kstate, ustate, vpkru);
- if (ret)
- return ret;
-
- /* Retrieve PKRU if not in init state */
- if (kstate->regs.xsave.header.xfeatures & XFEATURE_MASK_PKRU) {
- xpkru = get_xsave_addr(&kstate->regs.xsave, XFEATURE_PKRU);
- *vpkru = xpkru->pkru;
- }
- return 0;
+ return copy_uabi_from_kernel_to_xstate(kstate, ustate, vpkru);
}
EXPORT_SYMBOL_GPL(fpu_copy_uabi_to_guest_fpstate);
#endif /* CONFIG_KVM */
--- a/arch/x86/kernel/fpu/xstate.c
+++ b/arch/x86/kernel/fpu/xstate.c
@@ -1205,10 +1205,22 @@ static int copy_from_buffer(void *dst, u
* @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: unused
+ * @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 three 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.
+ * 3. When called from KVM the PKRU register will be restored from the vcpu's
+ * pkru field. A pointer to that is passed in @pkru.
*/
static int copy_uabi_to_xstate(struct fpstate *fpstate, const void *kbuf,
const void __user *ubuf, u32 *pkru)
@@ -1260,6 +1272,13 @@ static int copy_uabi_to_xstate(struct fp
}
}
+ 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':
