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author | Sean Christopherson <sean.j.christopherson@intel.com> | 2018-08-17 10:27:36 -0700 |
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committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2018-08-18 10:48:00 +0200 |
commit | 3f2e4f5dd83478b41ee273a500477cbf20266d23 (patch) | |
tree | 896a266bda1dd1ad6c1efdf682b48febbd8c1506 /arch | |
parent | 7251bd56d92540ab75d660e96d4fb1b7131b38da (diff) | |
download | linux-stable-3f2e4f5dd83478b41ee273a500477cbf20266d23.tar.gz linux-stable-3f2e4f5dd83478b41ee273a500477cbf20266d23.tar.bz2 linux-stable-3f2e4f5dd83478b41ee273a500477cbf20266d23.zip |
x86/speculation/l1tf: Exempt zeroed PTEs from inversion
commit f19f5c49bbc3ffcc9126cc245fc1b24cc29f4a37 upstream.
It turns out that we should *not* invert all not-present mappings,
because the all zeroes case is obviously special.
clear_page() does not undergo the XOR logic to invert the address bits,
i.e. PTE, PMD and PUD entries that have not been individually written
will have val=0 and so will trigger __pte_needs_invert(). As a result,
{pte,pmd,pud}_pfn() will return the wrong PFN value, i.e. all ones
(adjusted by the max PFN mask) instead of zero. A zeroed entry is ok
because the page at physical address 0 is reserved early in boot
specifically to mitigate L1TF, so explicitly exempt them from the
inversion when reading the PFN.
Manifested as an unexpected mprotect(..., PROT_NONE) failure when called
on a VMA that has VM_PFNMAP and was mmap'd to as something other than
PROT_NONE but never used. mprotect() sends the PROT_NONE request down
prot_none_walk(), which walks the PTEs to check the PFNs.
prot_none_pte_entry() gets the bogus PFN from pte_pfn() and returns
-EACCES because it thinks mprotect() is trying to adjust a high MMIO
address.
[ This is a very modified version of Sean's original patch, but all
credit goes to Sean for doing this and also pointing out that
sometimes the __pte_needs_invert() function only gets the protection
bits, not the full eventual pte. But zero remains special even in
just protection bits, so that's ok. - Linus ]
Fixes: f22cc87f6c1f ("x86/speculation/l1tf: Invert all not present mappings")
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Acked-by: Andi Kleen <ak@linux.intel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'arch')
-rw-r--r-- | arch/x86/include/asm/pgtable-invert.h | 11 |
1 files changed, 10 insertions, 1 deletions
diff --git a/arch/x86/include/asm/pgtable-invert.h b/arch/x86/include/asm/pgtable-invert.h index 44b1203ece12..a0c1525f1b6f 100644 --- a/arch/x86/include/asm/pgtable-invert.h +++ b/arch/x86/include/asm/pgtable-invert.h @@ -4,9 +4,18 @@ #ifndef __ASSEMBLY__ +/* + * A clear pte value is special, and doesn't get inverted. + * + * Note that even users that only pass a pgprot_t (rather + * than a full pte) won't trigger the special zero case, + * because even PAGE_NONE has _PAGE_PROTNONE | _PAGE_ACCESSED + * set. So the all zero case really is limited to just the + * cleared page table entry case. + */ static inline bool __pte_needs_invert(u64 val) { - return !(val & _PAGE_PRESENT); + return val && !(val & _PAGE_PRESENT); } /* Get a mask to xor with the page table entry to get the correct pfn. */ |