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linux-user: Don't assert if guest tries shmdt(0)

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Our implementation of shmat() and shmdt() for linux-user was
using "zero guest address" as its marker for "entry in the
shm_regions[] array is not in use". This meant that if the
guest did a shmdt(0) we would match on an unused array entry
and call page_set_flags() with both start and end addresses zero,
which causes an assertion failure.

Use an explicit in_use flag to manage the shm_regions[] array,
so that we avoid this problem.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reported-by: Pavel Shamis <pasharesearch@gmail.com>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Signed-off-by: Riku Voipio <riku.voipio@linaro.org>
This commit is contained in:
Peter Maydell 2016-02-09 15:57:11 +00:00 committed by Riku Voipio
parent de3f1b9841
commit b6e17875f2
1 changed files with 7 additions and 5 deletions
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12
linux-user/syscall.c
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@ -2598,8 +2598,9 @@ static abi_long do_socketcall(int num, abi_ulong vptr)
#define N_SHM_REGIONS 32
static struct shm_region {
abi_ulong start;
abi_ulong size;
abi_ulong start;
abi_ulong size;
bool in_use;
} shm_regions[N_SHM_REGIONS];
struct target_semid_ds
@ -3291,7 +3292,8 @@ static inline abi_ulong do_shmat(int shmid, abi_ulong shmaddr, int shmflg)
((shmflg & SHM_RDONLY)? 0 : PAGE_WRITE));
for (i = 0; i < N_SHM_REGIONS; i++) {
if (shm_regions[i].start == 0) {
if (!shm_regions[i].in_use) {
shm_regions[i].in_use = true;
shm_regions[i].start = raddr;
shm_regions[i].size = shm_info.shm_segsz;
break;
@ -3308,8 +3310,8 @@ static inline abi_long do_shmdt(abi_ulong shmaddr)
int i;
for (i = 0; i < N_SHM_REGIONS; ++i) {
if (shm_regions[i].start == shmaddr) {
shm_regions[i].start = 0;
if (shm_regions[i].in_use && shm_regions[i].start == shmaddr) {
shm_regions[i].in_use = false;
page_set_flags(shmaddr, shmaddr + shm_regions[i].size, 0);
break;
}