On Tue, Jan 28, 2025 at 06:58:06AM -0800, Eyal Birger wrote:
Note: uretprobe isn't supported in i386 and __NR_ia32_rt_tgsigqueueinfo uses the same number as __NR_uretprobe so the syscall isn't forced in the compat bitmap.
So a 64-bit tracer cannot use uretprobe on a 32-bit process? Also is uretprobe strictly an x86_64 feature?
[...] diff --git a/kernel/seccomp.c b/kernel/seccomp.c index 385d48293a5f..23b594a68bc0 100644 --- a/kernel/seccomp.c +++ b/kernel/seccomp.c @@ -734,13 +734,13 @@ seccomp_prepare_user_filter(const char __user *user_filter) #ifdef SECCOMP_ARCH_NATIVE /**
- seccomp_is_const_allow - check if filter is constant allow with given data
*/
- seccomp_is_filter_const_allow - check if filter is constant allow with given data
- @fprog: The BPF programs
- @sd: The seccomp data to check against, only syscall number and arch
number are considered constant.-static bool seccomp_is_const_allow(struct sock_fprog_kern *fprog,
struct seccomp_data *sd)+static bool seccomp_is_filter_const_allow(struct sock_fprog_kern *fprog,
struct seccomp_data *sd){ unsigned int reg_value = 0; unsigned int pc; @@ -812,6 +812,21 @@ static bool seccomp_is_const_allow(struct sock_fprog_kern *fprog, return false; } +static bool seccomp_is_const_allow(struct sock_fprog_kern *fprog,
struct seccomp_data *sd)+{ +#ifdef __NR_uretprobe
- if (sd->nr == __NR_uretprobe
+#ifdef SECCOMP_ARCH_COMPAT
&& sd->arch != SECCOMP_ARCH_COMPAT+#endif
I don't like this because it's not future-proof enough. __NR_uretprobe may collide with other syscalls at some point. And if __NR_uretprobe_32 is ever implemented, the seccomp logic will be missing. I think this will work now and in the future:
#ifdef __NR_uretprobe # ifdef SECCOMP_ARCH_COMPAT if (sd->arch == SECCOMP_ARCH_COMPAT) { # ifdef __NR_uretprobe_32 if (sd->nr == __NR_uretprobe_32) return true; # endif } else # endif if (sd->nr == __NR_uretprobe) return true; #endif
Instead of doing a function rename dance, I think you can just stick the above into seccomp_is_const_allow() after the WARN().
Also please add a KUnit tests to cover this in tools/testing/selftests/seccomp/seccomp_bpf.c With at least these cases combinations below. Check each of:
- not using uretprobe passes - using uretprobe passes (and validates that uretprobe did work)
in each of the following conditions:
- default-allow filter - default-block filter - filter explicitly blocking __NR_uretprobe and nothing else - filter explicitly allowing __NR_uretprobe (and only other required syscalls)
Hm, is uretprobe expected to work on mips? Because if so, you'll need to do something similar to the mode1 checking in the !SECCOMP_ARCH_NATIVE version of seccomp_cache_check_allow().
(You can see why I really dislike having policy baked into seccomp!)
)return true;+#endif
- return seccomp_is_filter_const_allow(fprog, sd);
+}
static void seccomp_cache_prepare_bitmap(struct seccomp_filter *sfilter, void *bitmap, const void *bitmap_prev, size_t bitmap_size, int arch) @@ -1023,6 +1038,9 @@ static inline void seccomp_log(unsigned long syscall, long signr, u32 action, */ static const int mode1_syscalls[] = { __NR_seccomp_read, __NR_seccomp_write, __NR_seccomp_exit, __NR_seccomp_sigreturn, +#ifdef __NR_uretprobe
- __NR_uretprobe,
+#endif
It'd be nice to update mode1_syscalls_32 with __NR_uretprobe_32 even though it doesn't exist. (Is it _never_ planned to be implemented?) But then, maybe the chances of a compat mode1 seccomp process running under uretprobe is vanishingly small.
-1, /* negative terminated */ }; -- 2.43.0
-Kees