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[84.42.143.70]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-ab6e47a7b0fsm80550366b.12.2025.01.30.00.24.44 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 30 Jan 2025 00:24:46 -0800 (PST) From: Jiri Olsa X-Google-Original-From: Jiri Olsa Date: Thu, 30 Jan 2025 09:24:43 +0100 To: Eyal Birger Cc: Kees Cook , luto@amacapital.net, wad@chromium.org, oleg@redhat.com, mhiramat@kernel.org, andrii@kernel.org, alexei.starovoitov@gmail.com, olsajiri@gmail.com, cyphar@cyphar.com, songliubraving@fb.com, yhs@fb.com, john.fastabend@gmail.com, peterz@infradead.org, tglx@linutronix.de, bp@alien8.de, daniel@iogearbox.net, ast@kernel.org, andrii.nakryiko@gmail.com, rostedt@goodmis.org, rafi@rbk.io, shmulik.ladkani@gmail.com, bpf@vger.kernel.org, linux-api@vger.kernel.org, linux-trace-kernel@vger.kernel.org, x86@kernel.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org Subject: Re: [PATCH v2] seccomp: passthrough uretprobe systemcall without filtering Message-ID: References: <20250128145806.1849977-1-eyal.birger@gmail.com> <202501281634.7F398CEA87@keescook> Precedence: bulk X-Mailing-List: linux-api@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: On Wed, Jan 29, 2025 at 09:27:49AM -0800, Eyal Birger wrote: > Hi, > > Thanks for the review! > > On Tue, Jan 28, 2025 at 5:41 PM Kees Cook wrote: > > > > 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? > > > > My understanding is that they'd be able to do so, but use the int3 trap > instead of the uretprobe syscall. > > > > [...] > > > 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. > > I'm not sure I got this 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 > > I don't know if implementing uretprobe syscall for compat binaries is > planned or makes sense - I'd appreciate Jiri's and others opinion on that. > That said, I don't mind adding this code for the sake of future proofing. as Andrii wrote in the other email ATM it's just strictly x86_64, but let's future proof it AFAIK there was an attempt to do similar on arm but it did not show any speed up > > > > > Instead of doing a function rename dance, I think you can just stick > > the above into seccomp_is_const_allow() after the WARN(). > > My motivation for the renaming dance was that you mentioned we might add > new syscalls to this as well, so I wanted to avoid cluttering the existing > function which seems to be well defined. > > > > > Also please add a KUnit tests to cover this in > > tools/testing/selftests/seccomp/seccomp_bpf.c > > I think this would mean that this test suite would need to run as > privileged. Is that Ok? or maybe it'd be better to have a new suite? > > > 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) > > Ok. please let me know if I can help in any way with tests > > > > > 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(). > > I don't know if uretprobe syscall is expected to run on mips. Personally > I'd avoid adding this dead code. > > > > > (You can see why I really dislike having policy baked into seccomp!) > > I definitely understand :) > > > > > > + ) > > > + 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. no plans for __NR_uretprobe_32 at this point > > It seems to me very unlikely. BTW, when I tested the "strict" mode change > my program was killed by seccomp. The reason wasn't the uretprobe syscall > (which I added to the list), it was actually the exit_group syscall which > libc uses instead of the exit syscall. > > Thanks again, > Eyal. thanks, jirka