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

[Paolo Bonzini <pbonzini@redhat.com>]

On 23/04/2018 18:25, Philippe Mathieu-Daudé wrote:
> 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 <peter.maydell@linaro.org>
> Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
> ---
>  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);
> 

Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>