Messages in this thread Patch in this message | | | From | Xiongfeng Wang <> | Subject | [Question] About SECCOMP issue for ILP32 | Date | Mon, 31 Aug 2020 20:48:05 +0800 |
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Hi Yury,
We were testing the ILP32 feature and came accross a problem. Very apperaciate it if you could give us some help !
We compile the LTP testsuite with '-mabi=ilp32' and run it on a machine with kernel and glibc applied with ILP32 patches. But we failed on one testcase, prctl04. It print the following error info. 'prctl04.c:199: FAIL: SECCOMP_MODE_STRICT doesn't permit read(2) write(2) and _exit(2)'
The testcase is like below, syscall 'prctl' followed by a syscall 'write'. prctl(PR_SET_SECCOMP, SECCOMP_MODE_STRICT); SAFE_WRITE(1, fd, "a", 1);
When we execute syscall 'write', we receive a SIGKILL. It's not as expected. We track the kernel and found out it is because we failed the syscall_whitelist check in '__secure_computing_strict'. Because flag 'TIF_32BIT_AARCH64' is set, we falls into the 'in_compat_syscall()' branch. We compare the parameter 'this_syscall' with return value of 'get_compat_model_syscalls()' The syscall number of '__NR_write' for ilp32 application is 64, but it is 4 for 'model_syscalls_32' returned from 'get_compat_model_syscalls()' So '__secure_computing_strict' retuned with 'do_exit(SIGKILL)'. We have a modification like below, but I am not sure if it correct or not.
--- a/kernel/seccomp.c +++ b/kernel/seccomp.c @@ -618,7 +618,7 @@ static void __secure_computing_strict(int this_syscall) { const int *syscall_whitelist = mode1_syscalls; #ifdef CONFIG_COMPAT - if (in_compat_syscall()) + if (is_a32_compat_task()) syscall_whitelist = get_compat_mode1_syscalls(); #endif do {
Thanks, Xiongfeng
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