On 06.01.18 21:51, Laurent Vivier wrote:
> Le 06/01/2018 à 18:00, 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 <[email protected]>
>> CC: Laurent Vivier <[email protected]>
>> CC: Peter Maydell <[email protected]>
>> Signed-off-by: Maximilian Riemensberger <[email protected]>
>> ---
>> 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;
>> }
>
> I think this is correct, but it would be clearer to not exit the loop if
> addr is NULL, something like:
>
> @@ -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;
>
> The result is the same because with the "addr -= qemu_host_page_size"
> addr becomes greater than end_addr on the next loop.
Sure. This patch also fixes the problem for me. Should I respin
or do you send this patch directly?
Thanks.
Max
>
> Thanks,
> Laurent
>
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