[tip: x86/fpu] x86/fpu: Add sanity checks for XFD
From: tip-bot2 for Thomas Gleixner
Date: Tue Oct 26 2021 - 12:17:14 EST
The following commit has been merged into the x86/fpu branch of tip:
Commit-ID: 5529acf47ec31ece0815f69d43f5e6a1e485a0f3
Gitweb: https://git.kernel.org/tip/5529acf47ec31ece0815f69d43f5e6a1e485a0f3
Author: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
AuthorDate: Thu, 21 Oct 2021 15:55:19 -07:00
Committer: Borislav Petkov <bp@xxxxxxx>
CommitterDate: Tue, 26 Oct 2021 10:52:35 +02:00
x86/fpu: Add sanity checks for XFD
Add debug functionality to ensure that the XFD MSR is up to date for XSAVE*
and XRSTOR* operations.
[ tglx: Improve comment. ]
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Chang S. Bae <chang.seok.bae@xxxxxxxxx>
Signed-off-by: Borislav Petkov <bp@xxxxxxx>
Link: https://lkml.kernel.org/r/20211021225527.10184-16-chang.seok.bae@xxxxxxxxx
---
arch/x86/kernel/fpu/core.c | 9 ++---
arch/x86/kernel/fpu/signal.c | 6 ++--
arch/x86/kernel/fpu/xstate.c | 58 +++++++++++++++++++++++++++++++++++-
arch/x86/kernel/fpu/xstate.h | 34 ++++++++++++++++++---
4 files changed, 95 insertions(+), 12 deletions(-)
diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
index 3b72cdd..b5f5b08 100644
--- a/arch/x86/kernel/fpu/core.c
+++ b/arch/x86/kernel/fpu/core.c
@@ -166,7 +166,7 @@ void restore_fpregs_from_fpstate(struct fpstate *fpstate, u64 mask)
*/
mask = fpu_kernel_cfg.max_features & mask;
- os_xrstor(&fpstate->regs.xsave, mask);
+ os_xrstor(fpstate, mask);
} else {
if (use_fxsr())
fxrstor(&fpstate->regs.fxsave);
@@ -534,7 +534,7 @@ void fpu__drop(struct fpu *fpu)
static inline void restore_fpregs_from_init_fpstate(u64 features_mask)
{
if (use_xsave())
- os_xrstor(&init_fpstate.regs.xsave, features_mask);
+ os_xrstor(&init_fpstate, features_mask);
else if (use_fxsr())
fxrstor(&init_fpstate.regs.fxsave);
else
@@ -591,9 +591,8 @@ void fpu__clear_user_states(struct fpu *fpu)
* corresponding registers.
*/
if (xfeatures_mask_supervisor() &&
- !fpregs_state_valid(fpu, smp_processor_id())) {
- os_xrstor(&fpu->fpstate->regs.xsave, xfeatures_mask_supervisor());
- }
+ !fpregs_state_valid(fpu, smp_processor_id()))
+ os_xrstor_supervisor(fpu->fpstate);
/* Reset user states in registers. */
restore_fpregs_from_init_fpstate(XFEATURE_MASK_USER_RESTORE);
diff --git a/arch/x86/kernel/fpu/signal.c b/arch/x86/kernel/fpu/signal.c
index 3b7f7d0..16fdecd 100644
--- a/arch/x86/kernel/fpu/signal.c
+++ b/arch/x86/kernel/fpu/signal.c
@@ -261,7 +261,7 @@ static int __restore_fpregs_from_user(void __user *buf, u64 ufeatures,
ret = fxrstor_from_user_sigframe(buf);
if (!ret && unlikely(init_bv))
- os_xrstor(&init_fpstate.regs.xsave, init_bv);
+ os_xrstor(&init_fpstate, init_bv);
return ret;
} else if (use_fxsr()) {
return fxrstor_from_user_sigframe(buf);
@@ -322,7 +322,7 @@ retry:
* been restored from a user buffer directly.
*/
if (test_thread_flag(TIF_NEED_FPU_LOAD) && xfeatures_mask_supervisor())
- os_xrstor(&fpu->fpstate->regs.xsave, xfeatures_mask_supervisor());
+ os_xrstor_supervisor(fpu->fpstate);
fpregs_mark_activate();
fpregs_unlock();
@@ -432,7 +432,7 @@ static bool __fpu_restore_sig(void __user *buf, void __user *buf_fx,
u64 mask = user_xfeatures | xfeatures_mask_supervisor();
fpregs->xsave.header.xfeatures &= mask;
- success = !os_xrstor_safe(&fpregs->xsave,
+ success = !os_xrstor_safe(fpu->fpstate,
fpu_kernel_cfg.max_features);
} else {
success = !fxrstor_safe(&fpregs->fxsave);
diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c
index bf42ee2..603edeb 100644
--- a/arch/x86/kernel/fpu/xstate.c
+++ b/arch/x86/kernel/fpu/xstate.c
@@ -1301,6 +1301,64 @@ EXPORT_SYMBOL_GPL(fpstate_clear_xstate_component);
#endif
#ifdef CONFIG_X86_64
+
+#ifdef CONFIG_X86_DEBUG_FPU
+/*
+ * Ensure that a subsequent XSAVE* or XRSTOR* instruction with RFBM=@mask
+ * can safely operate on the @fpstate buffer.
+ */
+static bool xstate_op_valid(struct fpstate *fpstate, u64 mask, bool rstor)
+{
+ u64 xfd = __this_cpu_read(xfd_state);
+
+ if (fpstate->xfd == xfd)
+ return true;
+
+ /*
+ * The XFD MSR does not match fpstate->xfd. That's invalid when
+ * the passed in fpstate is current's fpstate.
+ */
+ if (fpstate->xfd == current->thread.fpu.fpstate->xfd)
+ return false;
+
+ /*
+ * XRSTOR(S) from init_fpstate are always correct as it will just
+ * bring all components into init state and not read from the
+ * buffer. XSAVE(S) raises #PF after init.
+ */
+ if (fpstate == &init_fpstate)
+ return rstor;
+
+ /*
+ * XSAVE(S): clone(), fpu_swap_kvm_fpu()
+ * XRSTORS(S): fpu_swap_kvm_fpu()
+ */
+
+ /*
+ * No XSAVE/XRSTOR instructions (except XSAVE itself) touch
+ * the buffer area for XFD-disabled state components.
+ */
+ mask &= ~xfd;
+
+ /*
+ * Remove features which are valid in fpstate. They
+ * have space allocated in fpstate.
+ */
+ mask &= ~fpstate->xfeatures;
+
+ /*
+ * Any remaining state components in 'mask' might be written
+ * by XSAVE/XRSTOR. Fail validation it found.
+ */
+ return !mask;
+}
+
+void xfd_validate_state(struct fpstate *fpstate, u64 mask, bool rstor)
+{
+ WARN_ON_ONCE(!xstate_op_valid(fpstate, mask, rstor));
+}
+#endif /* CONFIG_X86_DEBUG_FPU */
+
static int validate_sigaltstack(unsigned int usize)
{
struct task_struct *thread, *leader = current->group_leader;
diff --git a/arch/x86/kernel/fpu/xstate.h b/arch/x86/kernel/fpu/xstate.h
index 32a4dee..2902424 100644
--- a/arch/x86/kernel/fpu/xstate.h
+++ b/arch/x86/kernel/fpu/xstate.h
@@ -130,6 +130,12 @@ static inline u64 xfeatures_mask_independent(void)
: "D" (st), "m" (*st), "a" (lmask), "d" (hmask) \
: "memory")
+#if defined(CONFIG_X86_64) && defined(CONFIG_X86_DEBUG_FPU)
+extern void xfd_validate_state(struct fpstate *fpstate, u64 mask, bool rstor);
+#else
+static inline void xfd_validate_state(struct fpstate *fpstate, u64 mask, bool rstor) { }
+#endif
+
/*
* Save processor xstate to xsave area.
*
@@ -144,6 +150,7 @@ static inline void os_xsave(struct fpstate *fpstate)
int err;
WARN_ON_FPU(!alternatives_patched);
+ xfd_validate_state(fpstate, mask, false);
XSTATE_XSAVE(&fpstate->regs.xsave, lmask, hmask, err);
@@ -156,12 +163,23 @@ static inline void os_xsave(struct fpstate *fpstate)
*
* Uses XRSTORS when XSAVES is used, XRSTOR otherwise.
*/
-static inline void os_xrstor(struct xregs_state *xstate, u64 mask)
+static inline void os_xrstor(struct fpstate *fpstate, u64 mask)
+{
+ u32 lmask = mask;
+ u32 hmask = mask >> 32;
+
+ xfd_validate_state(fpstate, mask, true);
+ XSTATE_XRESTORE(&fpstate->regs.xsave, lmask, hmask);
+}
+
+/* Restore of supervisor state. Does not require XFD */
+static inline void os_xrstor_supervisor(struct fpstate *fpstate)
{
+ u64 mask = xfeatures_mask_supervisor();
u32 lmask = mask;
u32 hmask = mask >> 32;
- XSTATE_XRESTORE(xstate, lmask, hmask);
+ XSTATE_XRESTORE(&fpstate->regs.xsave, lmask, hmask);
}
/*
@@ -184,11 +202,14 @@ static inline int xsave_to_user_sigframe(struct xregs_state __user *buf)
* internally, e.g. PKRU. That's user space ABI and also required
* to allow the signal handler to modify PKRU.
*/
- u64 mask = current->thread.fpu.fpstate->user_xfeatures;
+ struct fpstate *fpstate = current->thread.fpu.fpstate;
+ u64 mask = fpstate->user_xfeatures;
u32 lmask = mask;
u32 hmask = mask >> 32;
int err;
+ xfd_validate_state(fpstate, mask, false);
+
stac();
XSTATE_OP(XSAVE, buf, lmask, hmask, err);
clac();
@@ -206,6 +227,8 @@ static inline int xrstor_from_user_sigframe(struct xregs_state __user *buf, u64
u32 hmask = mask >> 32;
int err;
+ xfd_validate_state(current->thread.fpu.fpstate, mask, true);
+
stac();
XSTATE_OP(XRSTOR, xstate, lmask, hmask, err);
clac();
@@ -217,12 +240,15 @@ static inline int xrstor_from_user_sigframe(struct xregs_state __user *buf, u64
* Restore xstate from kernel space xsave area, return an error code instead of
* an exception.
*/
-static inline int os_xrstor_safe(struct xregs_state *xstate, u64 mask)
+static inline int os_xrstor_safe(struct fpstate *fpstate, u64 mask)
{
+ struct xregs_state *xstate = &fpstate->regs.xsave;
u32 lmask = mask;
u32 hmask = mask >> 32;
int err;
+ /* Must enforce XFD update here */
+
if (cpu_feature_enabled(X86_FEATURE_XSAVES))
XSTATE_OP(XRSTORS, xstate, lmask, hmask, err);
else