[PATCH] x86/fpu: Set XFEATURE_PKRU when writing to pkru

[Brian Geffon]

On kernels prior to 5.14 the write_pkru path could
end up writing to the pkru register without updating
the corresponding state.

Signed-off-by: Brian Geffon <bgeffon@xxxxxxxxxx>
---
 arch/x86/include/asm/fpu/internal.h | 22 ++++++++++------------
 arch/x86/include/asm/pgtable.h      |  5 +++--
 2 files changed, 13 insertions(+), 14 deletions(-)

diff --git a/arch/x86/include/asm/fpu/internal.h
b/arch/x86/include/asm/fpu/internal.h
index 16bf4d4a8159..ed2ce7d1afeb 100644
--- a/arch/x86/include/asm/fpu/internal.h
+++ b/arch/x86/include/asm/fpu/internal.h
@@ -564,18 +564,16 @@ static inline void switch_fpu_finish(struct fpu *new_=
fpu)
         * PKRU state is switched eagerly because it needs to be valid befo=
re we
         * return to userland e.g. for a copy_to_user() operation.
         */
-       if (!(current->flags & PF_KTHREAD)) {
-               /*
-                * If the PKRU bit in xsave.header.xfeatures is not set,
-                * then the PKRU component was in init state, which means
-                * XRSTOR will set PKRU to 0. If the bit is not set then
-                * get_xsave_addr() will return NULL because the PKRU value
-                * in memory is not valid. This means pkru_val has to be
-                * set to 0 and not to init_pkru_value.
-                */
-               pk =3D get_xsave_addr(&new_fpu->state.xsave, XFEATURE_PKRU)=
;
-               pkru_val =3D pk ? pk->pkru : 0;
-       }
+       /*
+        * If the PKRU bit in xsave.header.xfeatures is not set,
+        * then the PKRU component was in init state, which means
+        * XRSTOR will set PKRU to 0. If the bit is not set then
+        * get_xsave_addr() will return NULL because the PKRU value
+        * in memory is not valid. This means pkru_val has to be
+        * set to 0 and not to init_pkru_value.
+        */
+       pk =3D get_xsave_addr(&new_fpu->state.xsave, XFEATURE_PKRU);
+       pkru_val =3D pk ? pk->pkru : 0;
        __write_pkru(pkru_val);
 }

diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.=
h
index b1099f2d9800..d00fc2df4cfe 100644
--- a/arch/x86/include/asm/pgtable.h
+++ b/arch/x86/include/asm/pgtable.h
@@ -137,18 +137,19 @@ static inline u32 read_pkru(void)
 static inline void write_pkru(u32 pkru)
 {
        struct pkru_state *pk;
+       struct fpu *fpu =3D &current->thread.fpu;

        if (!boot_cpu_has(X86_FEATURE_OSPKE))
                return;

-       pk =3D get_xsave_addr(&current->thread.fpu.state.xsave, XFEATURE_PK=
RU);
-
        /*
         * The PKRU value in xstate needs to be in sync with the value that=
 is
         * written to the CPU. The FPU restore on return to userland would
         * otherwise load the previous value again.
         */
+       fpu->state.xsave.header.xfeatures |=3D XFEATURE_MASK_PKRU;
        fpregs_lock();
+       pk =3D get_xsave_addr(&fpu->state.xsave, XFEATURE_PKRU);
        if (pk)
                pk->pkru =3D pkru;
        __write_pkru(pkru);
--=20
2.34.0.rc0.344.g81b53c2807-goog