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x86/mm/64: Stop using CR3.PCID == 0 in ASID-aware code
Putting the logical ASID into CR3's PCID bits directly means that we have two cases to consider separately: ASID == 0 and ASID != 0. This means that bugs that only hit in one of these cases trigger nondeterministically. There were some bugs like this in the past, and I think there's still one in current kernels. In particular, we have a number of ASID-unware code paths that save CR3, write some special value, and then restore CR3. This includes suspend/resume, hibernate, kexec, EFI, and maybe other things I've missed. This is currently dangerous: if ASID != 0, then this code sequence will leave garbage in the TLB tagged for ASID 0. We could potentially see corruption when switching back to ASID 0. In principle, an initialize_tlbstate_and_flush() call after these sequences would solve the problem, but EFI, at least, does not call this. (And it probably shouldn't -- initialize_tlbstate_and_flush() is rather expensive.) Signed-off-by: Andy Lutomirski <luto@kernel.org> Cc: Borislav Petkov <bpetkov@suse.de> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Link: http://lkml.kernel.org/r/cdc14bbe5d3c3ef2a562be09a6368ffe9bd947a6.1505663533.git.luto@kernel.org Signed-off-by: Ingo Molnar <mingo@kernel.org>
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1 changed files with 19 additions and 2 deletions
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@ -286,14 +286,31 @@ static inline bool arch_vma_access_permitted(struct vm_area_struct *vma,
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return __pkru_allows_pkey(vma_pkey(vma), write);
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}
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/*
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* If PCID is on, ASID-aware code paths put the ASID+1 into the PCID
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* bits. This serves two purposes. It prevents a nasty situation in
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* which PCID-unaware code saves CR3, loads some other value (with PCID
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* == 0), and then restores CR3, thus corrupting the TLB for ASID 0 if
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* the saved ASID was nonzero. It also means that any bugs involving
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* loading a PCID-enabled CR3 with CR4.PCIDE off will trigger
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* deterministically.
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*/
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static inline unsigned long build_cr3(struct mm_struct *mm, u16 asid)
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{
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return __sme_pa(mm->pgd) | asid;
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if (static_cpu_has(X86_FEATURE_PCID)) {
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VM_WARN_ON_ONCE(asid > 4094);
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return __sme_pa(mm->pgd) | (asid + 1);
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} else {
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VM_WARN_ON_ONCE(asid != 0);
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return __sme_pa(mm->pgd);
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}
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}
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static inline unsigned long build_cr3_noflush(struct mm_struct *mm, u16 asid)
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{
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return __sme_pa(mm->pgd) | asid | CR3_NOFLUSH;
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VM_WARN_ON_ONCE(asid > 4094);
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return __sme_pa(mm->pgd) | (asid + 1) | CR3_NOFLUSH;
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}
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/*
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