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x86/process: Check PF_KTHREAD and not current->mm for kernel threads

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switch_fpu_finish() checks current->mm as indicator for kernel threads.
That's wrong because kernel threads can temporarily use a mm of a user
process via kthread_use_mm().

Check the task flags for PF_KTHREAD instead.

Fixes: 0cecca9d03 ("x86/fpu: Eager switch PKRU state")
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Acked-by: Dave Hansen <dave.hansen@linux.intel.com>
Acked-by: Rik van Riel <riel@surriel.com>
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/20210608144345.912645927@linutronix.de
This commit is contained in:
Thomas Gleixner
2021-06-08 16:36:20 +02:00
committed by Borislav Petkov
parent d8778e393a
commit 12f7764ac6
1 changed files with 1 additions and 1 deletions
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2
arch/x86/include/asm/fpu/internal.h
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@@ -578,7 +578,7 @@ static inline void switch_fpu_finish(struct fpu *new_fpu)
* PKRU state is switched eagerly because it needs to be valid before we * PKRU state is switched eagerly because it needs to be valid before we
* return to userland e.g. for a copy_to_user() operation. * return to userland e.g. for a copy_to_user() operation.
*/ */
if (current->mm) { if (!(current->flags & PF_KTHREAD)) {
pk = get_xsave_addr(&new_fpu->state.xsave, XFEATURE_PKRU); pk = get_xsave_addr(&new_fpu->state.xsave, XFEATURE_PKRU);
if (pk) if (pk)
pkru_val = pk->pkru; pkru_val = pk->pkru;