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Re: [Qemu-devel] [PATCH] linux-user/mmap.c: Avoid choosing NULL as start
From: |
Maximilian Riemensberger |
Subject: |
Re: [Qemu-devel] [PATCH] linux-user/mmap.c: Avoid choosing NULL as start address |
Date: |
Sat, 6 Jan 2018 18:15:36 +0100 |
User-agent: |
Mozilla/5.0 (Macintosh; Intel Mac OS X 10.13; rv:52.0) Gecko/20100101 Thunderbird/52.5.2 |
On 06.01.18 18:00, Maximilian Riemensberger wrote:
> 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.
I should have added:
Fixes: 59e9d91c7ae1b655997aec61c08eec1685414117 ("linux-user: resolve
reserved_va vma downwards")
Cheers,
Max
>
> CC: Riku Voipio <address@hidden>
> CC: Laurent Vivier <address@hidden>
> CC: Peter Maydell <address@hidden>
> Signed-off-by: Maximilian Riemensberger <address@hidden>
> ---
> 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..20cc5a7 100644
> --- a/linux-user/mmap.c
> +++ b/linux-user/mmap.c
> @@ -221,7 +221,7 @@ static abi_ulong mmap_find_vma_reserved(abi_ulong start,
> abi_ulong size)
> addr = end_addr - qemu_host_page_size;
>
> while (1) {
> - if (addr > end_addr) {
> + if (!addr || addr > end_addr) {
> if (looped) {
> return (abi_ulong)-1;
> }
>
--
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