[PATCH blktests] src/sg/syzkaller1.c: fix portability problem for syscall(__NR_mmap, ...)

[PATCH blktests] src/sg/syzkaller1.c: fix portability problem for syscall(__NR_mmap, ...)

[Theodore Ts'o]

How mmap is mapped to a raw system call varies across different
archiecture.  On some architectures (such as 32-bit ARM), __NR_mmap
may not exist at all; glibc will use __NR_mmap2 to implement mmap(2).
Syzkaller is using mmap() as a non-portable version of malloc(3), so
it should be safe to use the glibc's mmap wrapper instead of trying to
directly call the system call.

Signed-off-by: Theodore Ts'o <tytso@mit.edu>
---
 src/sg/syzkaller1.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/src/sg/syzkaller1.c b/src/sg/syzkaller1.c
index 743859a..e254d4a 100644
--- a/src/sg/syzkaller1.c
+++ b/src/sg/syzkaller1.c
@@ -401,8 +401,10 @@ long r[15];
 void test()
 {
   memset(r, -1, sizeof(r));
-  r[0] = execute_syscall(__NR_mmap, 0x20000000ul, 0x5000ul, 0x3ul,
-                         0x32ul, (uintptr_t)(-1ul), 0x0ul, 0, 0, 0);
+//r[0] = execute_syscall(__NR_mmap, 0x20000000ul, 0x5000ul, 0x3ul,
+//                       0x32ul, (uintptr_t)(-1ul), 0x0ul, 0, 0, 0);
+  r[0] = (long) mmap((void *) 0x20000000, (size_t) 0x5000,
+                     PROT_READ | PROT_WRITE, MAP_FIXED | MAP_ANONYMOUS, -1, 0);
   NONFAILING(memcpy((void*)0x20000000,
                     dev_sg, strlen(dev_sg)));
   r[2] = execute_syscall(__NR_syz_open_dev, 0x20000000ul, 0x0ul, 0x2ul,
-- 
2.19.1

Re: [PATCH blktests] src/sg/syzkaller1.c: fix portability problem for syscall(__NR_mmap, ...)

[Bart Van Assche]

On 1/7/19 1:13 PM, Theodore Ts'o wrote:
> How mmap is mapped to a raw system call varies across different
> archiecture.  On some architectures (such as 32-bit ARM), __NR_mmap
   ^^^^^^^^^^^
   architectures?
> may not exist at all; glibc will use __NR_mmap2 to implement mmap(2).
> Syzkaller is using mmap() as a non-portable version of malloc(3), so
> it should be safe to use the glibc's mmap wrapper instead of trying to
> directly call the system call.
> 
> Signed-off-by: Theodore Ts'o <tytso@mit.edu>
> ---
>   src/sg/syzkaller1.c | 6 ++++--
>   1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/src/sg/syzkaller1.c b/src/sg/syzkaller1.c
> index 743859a..e254d4a 100644
> --- a/src/sg/syzkaller1.c
> +++ b/src/sg/syzkaller1.c
> @@ -401,8 +401,10 @@ long r[15];
>   void test()
>   {
>     memset(r, -1, sizeof(r));
> -  r[0] = execute_syscall(__NR_mmap, 0x20000000ul, 0x5000ul, 0x3ul,
> -                         0x32ul, (uintptr_t)(-1ul), 0x0ul, 0, 0, 0);
> +//r[0] = execute_syscall(__NR_mmap, 0x20000000ul, 0x5000ul, 0x3ul,
> +//                       0x32ul, (uintptr_t)(-1ul), 0x0ul, 0, 0, 0);
> +  r[0] = (long) mmap((void *) 0x20000000, (size_t) 0x5000,
> +                     PROT_READ | PROT_WRITE, MAP_FIXED | MAP_ANONYMOUS, -1, 0);
>     NONFAILING(memcpy((void*)0x20000000,
>                       dev_sg, strlen(dev_sg)));
>     r[2] = execute_syscall(__NR_syz_open_dev, 0x20000000ul, 0x0ul, 0x2ul,

Anyway:

Reviewed-by: Bart Van Assche <bvanassche@acm.org>