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

Commit Message

Greg Kroah-Hartman June 9, 2019, 4:42 p.m. UTC

From: Paul Burton <[e-mail]>

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 <[e-mail]>
Reported-by: Julien Cristau <[e-mail]>
Reviewed-by: Philippe Mathieu-Daudé <[e-mail]>
Tested-by: YunQiang Su <[e-mail]>
URL: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=929366
Cc: [e-mail] # v4.12+
Cc: [e-mail]
Cc: Yunqiang Su <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

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

Patch

--- 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);