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authorGreg Hackmann <ghackmann@android.com>2018-08-15 22:51:21 +0300
committerWill Deacon <will.deacon@arm.com>2018-08-17 12:27:14 +0300
commit5ad356eabc47d26a92140a0c4b20eba471c10de3 (patch)
tree7a29e934fefae3a9d0d655e86d8b1f399388191b /arch/arm64
parentf6cc0c50164994afd538911603b4a8f8029aeba7 (diff)
downloadlinux-5ad356eabc47d26a92140a0c4b20eba471c10de3.tar.xz
arm64: mm: check for upper PAGE_SHIFT bits in pfn_valid()
ARM64's pfn_valid() shifts away the upper PAGE_SHIFT bits of the input before seeing if the PFN is valid. This leads to false positives when some of the upper bits are set, but the lower bits match a valid PFN. For example, the following userspace code looks up a bogus entry in /proc/kpageflags: int pagemap = open("/proc/self/pagemap", O_RDONLY); int pageflags = open("/proc/kpageflags", O_RDONLY); uint64_t pfn, val; lseek64(pagemap, [...], SEEK_SET); read(pagemap, &pfn, sizeof(pfn)); if (pfn & (1UL << 63)) { /* valid PFN */ pfn &= ((1UL << 55) - 1); /* clear flag bits */ pfn |= (1UL << 55); lseek64(pageflags, pfn * sizeof(uint64_t), SEEK_SET); read(pageflags, &val, sizeof(val)); } On ARM64 this causes the userspace process to crash with SIGSEGV rather than reading (1 << KPF_NOPAGE). kpageflags_read() treats the offset as valid, and stable_page_flags() will try to access an address between the user and kernel address ranges. Fixes: c1cc1552616d ("arm64: MMU initialisation") Cc: stable@vger.kernel.org Signed-off-by: Greg Hackmann <ghackmann@google.com> Signed-off-by: Will Deacon <will.deacon@arm.com>
Diffstat (limited to 'arch/arm64')
-rw-r--r--arch/arm64/mm/init.c6
1 files changed, 5 insertions, 1 deletions
diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
index 325cfb3b858a..811f9f8b3bb0 100644
--- a/arch/arm64/mm/init.c
+++ b/arch/arm64/mm/init.c
@@ -287,7 +287,11 @@ static void __init zone_sizes_init(unsigned long min, unsigned long max)
#ifdef CONFIG_HAVE_ARCH_PFN_VALID
int pfn_valid(unsigned long pfn)
{
- return memblock_is_map_memory(pfn << PAGE_SHIFT);
+ phys_addr_t addr = pfn << PAGE_SHIFT;
+
+ if ((addr >> PAGE_SHIFT) != pfn)
+ return 0;
+ return memblock_is_map_memory(addr);
}
EXPORT_SYMBOL(pfn_valid);
#endif