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From: Laurent Vivier <laurent@vivier.eu>
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Date: Fri, 19 Jan 2018 17:34:37 +0100
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Subject: Re: [Qemu-devel] [PATCH v2] linux-user/mmap.c: Avoid choosing NULL
 as start address
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To: Maximilian Riemensberger <riemensberger@cadami.net>, qemu-devel <qemu-devel@nongnu.org>
Cc: Peter Maydell <peter.maydell@linaro.org>, Riku Voipio <riku.voipio@iki.fi>

Le 07/01/2018 à 02:01, Maximilian Riemensberger a écrit :
> mmap() is required by the linux kernel ABI and POSIX to return a
> non-NULL address when the implementation chooses a start address for the
> mapping.
> 
> The current implementation of mmap_find_vma_reserved() can return NULL
> as start address of a mapping which leads to subsequent crashes inside
> the guests glibc, e.g. output of qemu-arm-static --strace executing a
> test binary stx_test:
> 
>     1879 mmap2(NULL,8388608,PROT_READ|PROT_WRITE,MAP_PRIVATE|MAP_ANONYMOUS|0x20000,-1,0) = 0x00000000
>     1879 write(2,0xf6fd39d0,79) stx_test: allocatestack.c:514: allocate_stack: Assertion `mem != NULL' failed.
> 
> This patch fixes mmap_find_vma_reserved() by skipping NULL as start
> address while searching for a suitable mapping start address.
> 
> CC: Riku Voipio <riku.voipio@iki.fi>
> CC: Laurent Vivier <laurent@vivier.eu>
> CC: Peter Maydell <peter.maydell@linaro.org>
> Signed-off-by: Maximilian Riemensberger <riemensberger@cadami.net>
> ---
> Changes since v1:
>     - Applied feedback from Laurent Vivier
> 
>  linux-user/mmap.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/linux-user/mmap.c b/linux-user/mmap.c
> index 4888f53..0fbfd6d 100644
> --- a/linux-user/mmap.c
> +++ b/linux-user/mmap.c
> @@ -234,7 +234,7 @@ static abi_ulong mmap_find_vma_reserved(abi_ulong start, abi_ulong size)
>          if (prot) {
>              end_addr = addr;
>          }
> -        if (addr + size == end_addr) {
> +        if (addr && addr + size == end_addr) {
>              break;
>          }
>          addr -= qemu_host_page_size;
> 

Applied to my linux-user branch.

Thanks,
Laurent