From: Greg Hackmann <ghackmann@android.com>
To: linux-arm-kernel@lists.infradead.org
Cc: kernel-team@android.com, Greg Hackmann <ghackmann@google.com>,
stable@vger.kernel.org, Catalin Marinas <catalin.marinas@arm.com>,
Will Deacon <will.deacon@arm.com>,
Laura Abbott <labbott@redhat.com>,
Andrew Morton <akpm@linux-foundation.org>,
Robin Murphy <robin.murphy@arm.com>,
Johannes Weiner <hannes@cmpxchg.org>,
Kristina Martsenko <kristina.martsenko@arm.com>,
CHANDAN VN <chandan.vn@samsung.com>,
Steve Capper <steve.capper@arm.com>,
Stefan Agner <stefan@agner.ch>,
linux-kernel@vger.kernel.org
Subject: [PATCH v2 1/2] arm64: mm: check for upper PAGE_SHIFT bits in pfn_valid()
Date: Wed, 15 Aug 2018 12:51:21 -0700 [thread overview]
Message-ID: <20180815195123.187373-1-ghackmann@google.com> (raw)
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>
---
arch/arm64/mm/init.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)
diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
index 9abf8a1e7b25..787e27964ab9 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
--
2.18.0.865.gffc8e1a3cd6-goog
next reply other threads:[~2018-08-15 19:53 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-08-15 19:51 Greg Hackmann [this message]
2018-08-15 19:51 ` [PATCH v2 2/2] arm: mm: check for upper PAGE_SHIFT bits in pfn_valid() Greg Hackmann
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