3.16.62-rc1 review patch. If anyone has any objections, please let me know.
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From: Greg Hackmann ghackmann@android.com
commit 5ad356eabc47d26a92140a0c4b20eba471c10de3 upstream.
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") Signed-off-by: Greg Hackmann ghackmann@google.com Signed-off-by: Will Deacon will.deacon@arm.com [bwh: Backported to 3.16: Keep using memblock_is_memory()] Signed-off-by: Ben Hutchings ben@decadent.org.uk --- arch/arm64/mm/init.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-)
--- a/arch/arm64/mm/init.c +++ b/arch/arm64/mm/init.c @@ -113,7 +113,11 @@ static void __init zone_sizes_init(unsig #ifdef CONFIG_HAVE_ARCH_PFN_VALID int pfn_valid(unsigned long pfn) { - return memblock_is_memory(pfn << PAGE_SHIFT); + phys_addr_t addr = pfn << PAGE_SHIFT; + + if ((addr >> PAGE_SHIFT) != pfn) + return 0; + return memblock_is_memory(addr); } EXPORT_SYMBOL(pfn_valid); #endif