Re: [Qemu-devel] [PATCH v4] loader: Fix misaligned member access

[Richard Henderson]

On 04/24/2018 12:21 PM, 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 the 64-bit access using the ldst (host) API, which uses a local
> copy on the stack, thus guaranteeing a safe aligned access.
> 
> This fixes the following ASan warning:
> 
>   $ 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>
> ---
> v4: do not change the 32-bit access, use ldq_he_p() for the 64-bit access
> v3: do not use memcpy(), incorrectly change ldl_he_p()
> v2: do not change the 32-bit access, use memcpy(), add comments (David Gibson)
> v1: use memcpy()

Reviewed-by: Richard Henderson <address@hidden>


r~