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authorCatalin Marinas <catalin.marinas@arm.com>2017-07-25 14:53:03 +0100
committerWill Deacon <will.deacon@arm.com>2017-08-04 13:26:11 +0100
commit6d332747fa5f0a6843b56b5b129168ba909336d1 (patch)
tree5d4029213884457d165c2bfd476ece7764490bdd /arch/arm64/mm
parentarm64: Use arch_timer_get_rate when trapping CNTFRQ_EL0 (diff)
downloadlinux-dev-6d332747fa5f0a6843b56b5b129168ba909336d1.tar.xz
linux-dev-6d332747fa5f0a6843b56b5b129168ba909336d1.zip
arm64: Fix potential race with hardware DBM in ptep_set_access_flags()
In a system with DBM (dirty bit management) capable agents there is a possible race between a CPU executing ptep_set_access_flags() (maybe non-DBM capable) and a hardware update of the dirty state (clearing of PTE_RDONLY). The scenario: a) the pte is writable (PTE_WRITE set), clean (PTE_RDONLY set) and old (PTE_AF clear) b) ptep_set_access_flags() is called as a result of a read access and it needs to set the pte to writable, clean and young (PTE_AF set) c) a DBM-capable agent, as a result of a different write access, is marking the entry as young (setting PTE_AF) and dirty (clearing PTE_RDONLY) The current ptep_set_access_flags() implementation would set the PTE_RDONLY bit in the resulting value overriding the DBM update and losing the dirty state. This patch fixes such race by setting PTE_RDONLY to the most permissive (lowest value) of the current entry and the new one. Fixes: 66dbd6e61a52 ("arm64: Implement ptep_set_access_flags() for hardware AF/DBM") Cc: Will Deacon <will.deacon@arm.com> Acked-by: Mark Rutland <mark.rutland@arm.com> Acked-by: Steve Capper <steve.capper@arm.com> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com> Signed-off-by: Will Deacon <will.deacon@arm.com>
Diffstat (limited to 'arch/arm64/mm')
-rw-r--r--arch/arm64/mm/fault.c15
1 files changed, 8 insertions, 7 deletions
diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
index c7861c9864e6..2509e4fe6992 100644
--- a/arch/arm64/mm/fault.c
+++ b/arch/arm64/mm/fault.c
@@ -163,26 +163,27 @@ int ptep_set_access_flags(struct vm_area_struct *vma,
/* only preserve the access flags and write permission */
pte_val(entry) &= PTE_AF | PTE_WRITE | PTE_DIRTY;
- /*
- * PTE_RDONLY is cleared by default in the asm below, so set it in
- * back if necessary (read-only or clean PTE).
- */
+ /* set PTE_RDONLY if actual read-only or clean PTE */
if (!pte_write(entry) || !pte_sw_dirty(entry))
pte_val(entry) |= PTE_RDONLY;
/*
* Setting the flags must be done atomically to avoid racing with the
- * hardware update of the access/dirty state.
+ * hardware update of the access/dirty state. The PTE_RDONLY bit must
+ * be set to the most permissive (lowest value) of *ptep and entry
+ * (calculated as: a & b == ~(~a | ~b)).
*/
+ pte_val(entry) ^= PTE_RDONLY;
asm volatile("// ptep_set_access_flags\n"
" prfm pstl1strm, %2\n"
"1: ldxr %0, %2\n"
- " and %0, %0, %3 // clear PTE_RDONLY\n"
+ " eor %0, %0, %3 // negate PTE_RDONLY in *ptep\n"
" orr %0, %0, %4 // set flags\n"
+ " eor %0, %0, %3 // negate final PTE_RDONLY\n"
" stxr %w1, %0, %2\n"
" cbnz %w1, 1b\n"
: "=&r" (old_pteval), "=&r" (tmp), "+Q" (pte_val(*ptep))
- : "L" (~PTE_RDONLY), "r" (pte_val(entry)));
+ : "L" (PTE_RDONLY), "r" (pte_val(entry)));
flush_tlb_fix_spurious_fault(vma, address);
return 1;