Re: [PATCH] arm64: Correctly bounds check virt_addr_valid

From: Laura Abbott
Date: Wed Sep 21 2016 - 13:43:36 EST

On 09/21/2016 10:28 AM, Laura Abbott wrote:
virt_addr_valid is supposed to return true if and only if virt_to_page
returns a valid page structure. The current macro does math on whatever
address is given and passes that to pfn_valid to verify. vmalloc and
module addresses can happen to generate a pfn that 'happens' to be
valid. Fix this by only performing the pfn_valid check on addresses that
have the potential to be valid.

Signed-off-by: Laura Abbott <labbott@xxxxxxxxxx>
This caused a bug at least twice in hardened usercopy so it is an
actual problem. A further TODO is full DEBUG_VIRTUAL support to
catch these types of mistakes.
arch/arm64/include/asm/memory.h | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/include/asm/memory.h b/arch/arm64/include/asm/memory.h
index 31b7322..f741e19 100644
--- a/arch/arm64/include/asm/memory.h
+++ b/arch/arm64/include/asm/memory.h
@@ -214,7 +214,7 @@ static inline void *phys_to_virt(phys_addr_t x)

#define virt_to_page(kaddr) pfn_to_page(__pa(kaddr) >> PAGE_SHIFT)
-#define virt_addr_valid(kaddr) pfn_valid(__pa(kaddr) >> PAGE_SHIFT)
+#define virt_addr_valid(kaddr) (((u64)kaddr) >= PAGE_OFFSET && pfn_valid(__pa(kaddr) >> PAGE_SHIFT))
#define __virt_to_pgoff(kaddr) (((u64)(kaddr) & ~PAGE_OFFSET) / PAGE_SIZE * sizeof(struct page))
#define __page_to_voff(kaddr) (((u64)(page) & ~VMEMMAP_START) * PAGE_SIZE / sizeof(struct page))
@@ -222,8 +222,8 @@ static inline void *phys_to_virt(phys_addr_t x)
#define page_to_virt(page) ((void *)((__page_to_voff(page)) | PAGE_OFFSET))
#define virt_to_page(vaddr) ((struct page *)((__virt_to_pgoff(vaddr)) | VMEMMAP_START))

-#define virt_addr_valid(kaddr) pfn_valid((((u64)(kaddr) & ~PAGE_OFFSET) \
+#define virt_addr_valid(kaddr) (((u64)kaddr) >= PAGE_OFFSET && pfn_valid((((u64)(kaddr) & ~PAGE_OFFSET) \

Bah, I realized I butchered the macro parenthesization. I'll fix that
in a v2. I'll wait for comments on this first.