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Re: [Qemu-devel] [PATCH] linux-user: Don't assert if guest tries shmdt(0
From: |
Laurent Vivier |
Subject: |
Re: [Qemu-devel] [PATCH] linux-user: Don't assert if guest tries shmdt(0) |
Date: |
Wed, 10 Feb 2016 19:39:30 +0100 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.5.0 |
Le 09/02/2016 16:57, Peter Maydell a écrit :
> 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
Is shmdt(0) valid ?
I mean, if shmat() is called with shmaddr equal to 0:
"the system chooses a suitable (unused) address at which
to attach the segment."
and
"The to-be-detached segment must be currently attached with shmaddr
equal to the value returned by the attaching shmat() call."
Did you check shmat() can return 0 ?
(I think our mmap_find_vma() cannot return 0)
Why don't you fail on shmdt(0) (EINVAL) ?
> 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 <address@hidden>
> Reported-by: Pavel Shamis <address@hidden>
> ---
> linux-user/syscall.c | 12 +++++++-----
> 1 file changed, 7 insertions(+), 5 deletions(-)
>
> diff --git a/linux-user/syscall.c b/linux-user/syscall.c
> index 54ce14a..f46abf7 100644
> --- a/linux-user/syscall.c
> +++ b/linux-user/syscall.c
> @@ -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;
> }
>