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x86/fpu: Preserve supervisor states in sanitize_restored_user_xstate()

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sanitize_restored_user_xstate() preserves the supervisor states only
when the fx_only argument is zero, which allows unprivileged user space
to put supervisor states back into init state.

Preserve them unconditionally.

 [ bp: Fix a typo or two in the text. ]

Fixes: 5d6b6a6f9b ("x86/fpu/xstate: Update sanitize_restored_xstate() for supervisor xstates")
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/20210618143444.438635017@linutronix.de
This commit is contained in:
Thomas Gleixner 2021-06-18 16:18:24 +02:00 committed by Borislav Petkov
parent 13311e7425
commit 9301982c42
1 changed files with 8 additions and 18 deletions
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26
arch/x86/kernel/fpu/signal.c
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@ -221,28 +221,18 @@ sanitize_restored_user_xstate(union fpregs_state *state,
if (use_xsave()) { if (use_xsave()) {
/* /*
* Note: we don't need to zero the reserved bits in the * Clear all feature bits which are not set in
* xstate_header here because we either didn't copy them at all, * user_xfeatures and clear all extended features
* or we checked earlier that they aren't set. * for fx_only mode.
*/ */
u64 mask = fx_only ? XFEATURE_MASK_FPSSE : user_xfeatures;
/* /*
* 'user_xfeatures' might have bits clear which are * Supervisor state has to be preserved. The sigframe
* set in header->xfeatures. This represents features that * restore can only modify user features, i.e. @mask
* were in init state prior to a signal delivery, and need * cannot contain them.
* to be reset back to the init state. Clear any user
* feature bits which are set in the kernel buffer to get
* them back to the init state.
*
* Supervisor state is unchanged by input from userspace.
* Ensure supervisor state bits stay set and supervisor
* state is not modified.
*/ */
if (fx_only) header->xfeatures &= mask | xfeatures_mask_supervisor();
header->xfeatures = XFEATURE_MASK_FPSSE;
else
header->xfeatures &= user_xfeatures |
xfeatures_mask_supervisor();
} }
if (use_fxsr()) { if (use_fxsr()) {