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Subject[PATCH 22/23] x86/fpu: Don't restore the FPU state directly from userland in __fpu__restore_sig()
Date
__fpu__restore_sig() restores the CPU's FPU state directly from
userland. If we restore registers on return to userland then we can't
load them directly from userland because a context switch/BH could
destroy them.

Restore the FPU registers after they have been copied from userland.
__fpregs_changes_begin() ensures that they are not modified while beeing
worked on. TIF_NEED_FPU_LOAD is clreared we want to keep our state, not
the saved state.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
arch/x86/include/asm/fpu/internal.h | 34 -----------------------------
arch/x86/kernel/fpu/signal.c | 33 ++++++++++++++++++----------
2 files changed, 22 insertions(+), 45 deletions(-)

diff --git a/arch/x86/include/asm/fpu/internal.h b/arch/x86/include/asm/fpu/internal.h
index 9e213a6703c84..5e86ff60a3a5c 100644
--- a/arch/x86/include/asm/fpu/internal.h
+++ b/arch/x86/include/asm/fpu/internal.h
@@ -137,28 +137,11 @@ static inline void copy_kernel_to_fxregs(struct fxregs_state *fx)
}
}

-static inline int copy_user_to_fxregs(struct fxregs_state __user *fx)
-{
- if (IS_ENABLED(CONFIG_X86_32))
- return user_insn(fxrstor %[fx], "=m" (*fx), [fx] "m" (*fx));
- else if (IS_ENABLED(CONFIG_AS_FXSAVEQ))
- return user_insn(fxrstorq %[fx], "=m" (*fx), [fx] "m" (*fx));
-
- /* See comment in copy_fxregs_to_kernel() below. */
- return user_insn(rex64/fxrstor (%[fx]), "=m" (*fx), [fx] "R" (fx),
- "m" (*fx));
-}
-
static inline void copy_kernel_to_fregs(struct fregs_state *fx)
{
kernel_insn(frstor %[fx], "=m" (*fx), [fx] "m" (*fx));
}

-static inline int copy_user_to_fregs(struct fregs_state __user *fx)
-{
- return user_insn(frstor %[fx], "=m" (*fx), [fx] "m" (*fx));
-}
-
static inline void copy_fxregs_to_kernel(struct fpu *fpu)
{
if (IS_ENABLED(CONFIG_X86_32))
@@ -333,23 +316,6 @@ static inline void copy_kernel_to_xregs(struct xregs_state *xstate, u64 mask)
XSTATE_XRESTORE(xstate, lmask, hmask);
}

-/*
- * Restore xstate from user space xsave area.
- */
-static inline int copy_user_to_xregs(struct xregs_state __user *buf, u64 mask)
-{
- struct xregs_state *xstate = ((__force struct xregs_state *)buf);
- u32 lmask = mask;
- u32 hmask = mask >> 32;
- int err;
-
- stac();
- XSTATE_OP(XRSTOR, xstate, lmask, hmask, err);
- clac();
-
- return err;
-}
-
/*
* These must be called with preempt disabled. Returns
* 'true' if the FPU state is still intact and we can
diff --git a/arch/x86/kernel/fpu/signal.c b/arch/x86/kernel/fpu/signal.c
index 179e2b19976ad..9720529859483 100644
--- a/arch/x86/kernel/fpu/signal.c
+++ b/arch/x86/kernel/fpu/signal.c
@@ -228,23 +228,30 @@ sanitize_restored_xstate(union fpregs_state *state,
/*
* Restore the extended state if present. Otherwise, restore the FP/SSE state.
*/
-static inline int copy_user_to_fpregs_zeroing(void __user *buf, u64 xbv, int fx_only)
+static void copy_to_fpregs_zeroing(struct fpu *fpu, u64 xbv, int fx_only)
{
+ __fpregs_changes_begin();
if (use_xsave()) {
- if ((unsigned long)buf % 64 || fx_only) {
+ if (fx_only) {
u64 init_bv = xfeatures_mask & ~XFEATURE_MASK_FPSSE;
+
copy_kernel_to_xregs(&init_fpstate.xsave, init_bv);
- return copy_user_to_fxregs(buf);
+ copy_kernel_to_fxregs(&fpu->state.fxsave);
} else {
u64 init_bv = xfeatures_mask & ~xbv;
+
if (unlikely(init_bv))
copy_kernel_to_xregs(&init_fpstate.xsave, init_bv);
- return copy_user_to_xregs(buf, xbv);
+ copy_kernel_to_xregs(&fpu->state.xsave, xbv);
}
} else if (use_fxsr()) {
- return copy_user_to_fxregs(buf);
- } else
- return copy_user_to_fregs(buf);
+ copy_kernel_to_fxregs(&fpu->state.fxsave);
+ } else {
+ copy_kernel_to_fregs(&fpu->state.fsave);
+ }
+ clear_thread_flag(TIF_NEED_FPU_LOAD);
+ fpregs_activate(fpu);
+ __fpregs_changes_end();
}

static int __fpu__restore_sig(void __user *buf, void __user *buf_fx, int size)
@@ -255,6 +262,7 @@ static int __fpu__restore_sig(void __user *buf, void __user *buf_fx, int size)
int state_size = fpu_kernel_xstate_size;
u64 xfeatures = 0;
int fx_only = 0;
+ int err = 0;

ia32_fxstate &= (IS_ENABLED(CONFIG_X86_32) ||
IS_ENABLED(CONFIG_IA32_EMULATION));
@@ -298,7 +306,6 @@ static int __fpu__restore_sig(void __user *buf, void __user *buf_fx, int size)
union fpregs_state *state;
void *tmp;
struct user_i387_ia32_struct env;
- int err = 0;

tmp = kmalloc(sizeof(*state) + fpu_kernel_xstate_size + 64, GFP_KERNEL);
if (!tmp)
@@ -327,12 +334,16 @@ static int __fpu__restore_sig(void __user *buf, void __user *buf_fx, int size)
} else {
/*
* For 64-bit frames and 32-bit fsave frames, restore the user
- * state to the registers directly (with exceptions handled).
+ * state from a copy in thread's fpu state.
*/
- if (copy_user_to_fpregs_zeroing(buf_fx, xfeatures, fx_only)) {
+ err = __copy_from_user(&fpu->state.xsave, buf_fx, state_size);
+ if (err) {
fpu__clear(fpu);
- return -1;
+ return -EFAULT;
}
+ if ((unsigned long)buf_fx % 64)
+ fx_only = 1;
+ copy_to_fpregs_zeroing(fpu, xfeatures, fx_only);
}

return 0;
--
2.19.1
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