From: Kyle Huey <me@xxxxxxxxxxxx>
commit 4a804c4f8356 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@xxxxxxxxxxxx>
Signed-off-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Link: https://lore.kernel.org/all/20221115230932.7126-5-khuey%40kylehuey.com
---
arch/x86/kernel/fpu/xstate.c | 30 ++++++++++++++++++++++++++++++
1 file changed, 30 insertions(+)
diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c
index 8abce8015b72..fe9050c60adc 100644
--- a/arch/x86/kernel/fpu/xstate.c
+++ b/arch/x86/kernel/fpu/xstate.c
@@ -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':
--
2.25.1
