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x86/fpu/signal: Let xrstor handle the features to init 

There is no reason to do an extra XRSTOR from init_fpstate for feature
bits which have been cleared by user space in the FX magic xfeatures
storage.

Just clear them in the task's XSTATE header and do a full restore which
will put these cleared features into init state.

There is no real difference in performance because the current code
already does a full restore when the xfeatures bits are preserved as the
signal frame setup has stored them, which is the full UABI feature set.

 [ bp: Use the negated mxcsr_feature_mask in the MXCSR check. ]

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20210623121457.804115017@linutronix.de
This commit is contained in:
Thomas Gleixner 2021-06-23 14:02:32 +02:00 committed by Borislav Petkov
parent fcb3635f50
commit 6f9866a166
1 changed files with 32 additions and 59 deletions
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91
arch/x86/kernel/fpu/signal.c
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@ -220,36 +220,6 @@ retry:
return 0;
}
static inline void
sanitize_restored_user_xstate(union fpregs_state *state,
struct user_i387_ia32_struct *ia32_env, u64 mask)
{
struct xregs_state *xsave = &state->xsave;
struct xstate_header *header = &xsave->header;
if (use_xsave()) {
/*
* Clear all feature bits which are not set in mask.
*
* Supervisor state has to be preserved. The sigframe
* restore can only modify user features, i.e. @mask
* cannot contain them.
*/
header->xfeatures &= mask | xfeatures_mask_supervisor();
}
if (use_fxsr()) {
/*
* mscsr reserved bits must be masked to zero for security
* reasons.
*/
xsave->i387.mxcsr &= mxcsr_feature_mask;
if (ia32_env)
convert_to_fxsr(&state->fxsave, ia32_env);
}
}
static int __restore_fpregs_from_user(void __user *buf, u64 xrestore,
bool fx_only)
{
@ -352,6 +322,8 @@ static int __fpu_restore_sig(void __user *buf, void __user *buf_fx,
fx_only = !fx_sw_user.magic1;
state_size = fx_sw_user.xstate_size;
user_xfeatures = fx_sw_user.xfeatures;
} else {
user_xfeatures = XFEATURE_MASK_FPSSE;
}
if (likely(!ia32_fxstate)) {
@ -395,54 +367,55 @@ static int __fpu_restore_sig(void __user *buf, void __user *buf_fx,
set_thread_flag(TIF_NEED_FPU_LOAD);
}
__fpu_invalidate_fpregs_state(fpu);
__cpu_invalidate_fpregs_state();
fpregs_unlock();
if (use_xsave() && !fx_only) {
u64 init_bv = xfeatures_mask_uabi() & ~user_xfeatures;
ret = copy_sigframe_from_user_to_xstate(&fpu->state.xsave, buf_fx);
if (ret)
return ret;
sanitize_restored_user_xstate(&fpu->state, &env, user_xfeatures);
fpregs_lock();
if (unlikely(init_bv))
os_xrstor(&init_fpstate.xsave, init_bv);
/*
* Restore previously saved supervisor xstates along with
* copied-in user xstates.
*/
ret = os_xrstor_safe(&fpu->state.xsave,
user_xfeatures | xfeatures_mask_supervisor());
} else {
ret = __copy_from_user(&fpu->state.fxsave, buf_fx, state_size);
if (ret)
if (__copy_from_user(&fpu->state.fxsave, buf_fx,
sizeof(fpu->state.fxsave)))
return -EFAULT;
sanitize_restored_user_xstate(&fpu->state, &env, user_xfeatures);
/* Reject invalid MXCSR values. */
if (fpu->state.fxsave.mxcsr & ~mxcsr_feature_mask)
return -EINVAL;
fpregs_lock();
if (use_xsave()) {
u64 init_bv;
/* Enforce XFEATURE_MASK_FPSSE when XSAVE is enabled */
if (use_xsave())
fpu->state.xsave.header.xfeatures |= XFEATURE_MASK_FPSSE;
}
init_bv = xfeatures_mask_uabi() & ~XFEATURE_MASK_FPSSE;
os_xrstor(&init_fpstate.xsave, init_bv);
}
/* Fold the legacy FP storage */
convert_to_fxsr(&fpu->state.fxsave, &env);
fpregs_lock();
if (use_xsave()) {
/*
* Remove all UABI feature bits not set in user_xfeatures
* from the memory xstate header which makes the full
* restore below bring them into init state. This works for
* fx_only mode as well because that has only FP and SSE
* set in user_xfeatures.
*
* Preserve supervisor states!
*/
u64 mask = user_xfeatures | xfeatures_mask_supervisor();
fpu->state.xsave.header.xfeatures &= mask;
ret = os_xrstor_safe(&fpu->state.xsave, xfeatures_mask_all);
} else {
ret = fxrstor_safe(&fpu->state.fxsave);
}
if (!ret)
if (likely(!ret))
fpregs_mark_activate();
else
fpregs_deactivate(fpu);
fpregs_unlock();
return ret;
}
static inline int xstate_sigframe_size(void)
{
return use_xsave() ? fpu_user_xstate_size + FP_XSTATE_MAGIC2_SIZE :