[PATCH 1/1] crash_dump: fix non-pae kdump kernel memory accesses

From: Jiri Slaby
Date: Fri Oct 23 2009 - 11:45:39 EST


Non-PAE 32-bit dump kernels may wrap an address around 4G and
poke unwanted space. ptes there are 32-bit long, and since
pfn << PAGE_SIZE may exceed this limit, high pfn bits are cropped
and wrong address mapped by kmap_atomic_pfn in copy_oldmem_page.

Don't allow this behavior in non-PAE kdump kernels by checking
pfns passed into copy_oldmem_page. In the case of failure,
userspace process gets EFAULT.

Signed-off-by: Jiri Slaby <jirislaby@xxxxxxxxx>
Cc: Vivek Goyal <vgoyal@xxxxxxxxxx>
Cc: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx>
Cc: Simon Horman <horms@xxxxxxxxxxxx>
Cc: Paul Mundt <lethal@xxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxx>
---
arch/x86/kernel/crash_dump_32.c | 16 ++++++++++++++++
1 files changed, 16 insertions(+), 0 deletions(-)

diff --git a/arch/x86/kernel/crash_dump_32.c b/arch/x86/kernel/crash_dump_32.c
index f7cdb3b..b78dab8 100644
--- a/arch/x86/kernel/crash_dump_32.c
+++ b/arch/x86/kernel/crash_dump_32.c
@@ -16,6 +16,19 @@ static void *kdump_buf_page;
/* Stores the physical address of elf header of crash image. */
unsigned long long elfcorehdr_addr = ELFCORE_ADDR_MAX;

+#ifndef CONFIG_X86_PAE
+/* non-PAE kdump kernel executed from a PAE one will crop high pte bits and
+ poke unwanted space counting again from address 0, we don't want that */
+static inline bool is_crashed_pfn_valid(unsigned long pfn)
+{
+ /* on non-PAE pte must fit into unsigned long
+ in fact the test is (pfn & 0x000fffff) */
+ return pte_pfn(pfn_pte(pfn, __pgprot(0))) == pfn;
+}
+#else
+static inline bool is_crashed_pfn_valid(unsigned long pfn) { return true; }
+#endif
+
/**
* copy_oldmem_page - copy one page from "oldmem"
* @pfn: page frame number to be copied
@@ -41,6 +54,9 @@ ssize_t copy_oldmem_page(unsigned long pfn, char *buf,
if (!csize)
return 0;

+ if (!is_crashed_pfn_valid(pfn))
+ return -EFAULT;
+
vaddr = kmap_atomic_pfn(pfn, KM_PTE0);

if (!userbuf) {
--
1.6.4.2

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