[Qemu-devel] [PATCH v3 2/2] loader: Fix 64-bit misaligned member access

[Philippe Mathieu-Daudé]

The libfdt does not guarantee than fdt_getprop() returns a pointer
aligned to the property size.

Assuming the base of the fdt is aligned, a 32-bit property returns
a 32-bit aligned pointer. This is however not guaranteed for 64-bit
properties, where 64-bit loads might trigger unaligned access.

Fix this issue by using the ldst (host) API, which does a local copy
on the stack, thus guaranteeing a safe aligned access.

This fixes the following ASan warning:

  $ mips64el-softmmu/qemu-system-mips64el -M boston -kernel vmlinux.gz.itb 
-nographic
  hw/core/loader-fit.c:108:17: runtime error: load of misaligned address 
0x7f95cd7e4264 for type 'fdt64_t', which requires 8 byte alignment
  0x7f95cd7e4264: note: pointer points here
    00 00 00 3e ff ff ff ff  80 7d 2a c0 00 00 00 01  68 61 73 68 40 30 00 00  
00 00 00 03 00 00 00 14
                ^

Reported-by: AddressSanitizer
Suggested-by: Peter Maydell <address@hidden>
Signed-off-by: Philippe Mathieu-Daudé <address@hidden>
---
 hw/core/loader-fit.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/hw/core/loader-fit.c b/hw/core/loader-fit.c
index 0c4a7207f4..628f854636 100644
--- a/hw/core/loader-fit.c
+++ b/hw/core/loader-fit.c
@@ -102,10 +102,10 @@ static int fit_image_addr(const void *itb, int img, const 
char *name,
 
     switch (len) {
     case 4:
-        *addr = fdt32_to_cpu(*(fdt32_t *)prop);
+        *addr = fdt32_to_cpu(ldl_he_p(prop));
         return 0;
     case 8:
-        *addr = fdt64_to_cpu(*(fdt64_t *)prop);
+        *addr = fdt64_to_cpu(ldq_he_p(prop));
         return 0;
     default:
         error_printf("invalid %s address length %d\n", name, len);
-- 
2.17.0