[PATCH 4.14 21/35] MIPS: Bounds check virt_addr_valid

* [PATCH 4.14 21/35] MIPS: Bounds check virt_addr_valid
       [not found] <20190609164125.377368385@linuxfoundation.org>
@ 2019-06-09 16:42 ` Greg Kroah-Hartman
  2019-06-09 16:42 ` [PATCH 4.14 22/35] MIPS: pistachio: Build uImage.gz by default Greg Kroah-Hartman
  2019-06-09 16:42 ` [PATCH 4.14 23/35] Revert "MIPS: perf: ath79: Fix perfcount IRQ assignment" Greg Kroah-Hartman
  2 siblings, 0 replies; 3+ messages in thread
From: Greg Kroah-Hartman @ 2019-06-09 16:42 UTC (permalink / raw)
  To: linux-kernel
  Cc: Greg Kroah-Hartman, stable, Paul Burton, Julien Cristau,
	Philippe Mathieu-Daudé,
	YunQiang Su, linux-mips

From: Paul Burton <paul.burton@mips.com>

commit 074a1e1167afd82c26f6d03a9a8b997d564bb241 upstream.

The virt_addr_valid() function is meant to return true iff
virt_to_page() will return a valid struct page reference. This is true
iff the address provided is found within the unmapped address range
between PAGE_OFFSET & MAP_BASE, but we don't currently check for that
condition. Instead we simply mask the address to obtain what will be a
physical address if the virtual address is indeed in the desired range,
shift it to form a PFN & then call pfn_valid(). This can incorrectly
return true if called with a virtual address which, after masking,
happens to form a physical address corresponding to a valid PFN.

For example we may vmalloc an address in the kernel mapped region
starting a MAP_BASE & obtain the virtual address:

  addr = 0xc000000000002000

When masked by virt_to_phys(), which uses __pa() & in turn CPHYSADDR(),
we obtain the following (bogus) physical address:

  addr = 0x2000

In a common system with PHYS_OFFSET=0 this will correspond to a valid
struct page which should really be accessed by virtual address
PAGE_OFFSET+0x2000, causing virt_addr_valid() to incorrectly return 1
indicating that the original address corresponds to a struct page.

This is equivalent to the ARM64 change made in commit ca219452c6b8
("arm64: Correctly bounds check virt_addr_valid").

This fixes fallout when hardened usercopy is enabled caused by the
related commit 517e1fbeb65f ("mm/usercopy: Drop extra
is_vmalloc_or_module() check") which removed a check for the vmalloc
range that was present from the introduction of the hardened usercopy
feature.

Signed-off-by: Paul Burton <paul.burton@mips.com>
Reported-by: Julien Cristau <jcristau@debian.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Tested-by: YunQiang Su <ysu@wavecomp.com>
URL: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=929366
Cc: stable@vger.kernel.org # v4.12+
Cc: linux-mips@vger.kernel.org
Cc: Yunqiang Su <ysu@wavecomp.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 arch/mips/mm/mmap.c |    5 +++++
 1 file changed, 5 insertions(+)

--- a/arch/mips/mm/mmap.c
+++ b/arch/mips/mm/mmap.c
@@ -203,6 +203,11 @@ unsigned long arch_randomize_brk(struct
 
 int __virt_addr_valid(const volatile void *kaddr)
 {
+	unsigned long vaddr = (unsigned long)vaddr;
+
+	if ((vaddr < PAGE_OFFSET) || (vaddr >= MAP_BASE))
+		return 0;
+
 	return pfn_valid(PFN_DOWN(virt_to_phys(kaddr)));
 }
 EXPORT_SYMBOL_GPL(__virt_addr_valid);



^ permalink raw reply	[flat|nested] 3+ messages in thread