Bugzilla – Bug 1225079
VUL-0: CVE-2023-52828: kernel: bpf: Detect IP == ksym.end as part of BPF program
Last modified: 2024-07-10 08:46:02 UTC
In the Linux kernel, the following vulnerability has been resolved: bpf: Detect IP == ksym.end as part of BPF program Now that bpf_throw kfunc is the first such call instruction that has noreturn semantics within the verifier, this also kicks in dead code elimination in unprecedented ways. For one, any instruction following a bpf_throw call will never be marked as seen. Moreover, if a callchain ends up throwing, any instructions after the call instruction to the eventually throwing subprog in callers will also never be marked as seen. The tempting way to fix this would be to emit extra 'int3' instructions which bump the jited_len of a program, and ensure that during runtime when a program throws, we can discover its boundaries even if the call instruction to bpf_throw (or to subprogs that always throw) is emitted as the final instruction in the program. An example of such a program would be this: do_something(): ... r0 = 0 exit foo(): r1 = 0 call bpf_throw r0 = 0 exit bar(cond): if r1 != 0 goto pc+2 call do_something exit call foo r0 = 0 // Never seen by verifier exit // main(ctx): r1 = ... call bar r0 = 0 exit Here, if we do end up throwing, the stacktrace would be the following: bpf_throw foo bar main In bar, the final instruction emitted will be the call to foo, as such, the return address will be the subsequent instruction (which the JIT emits as int3 on x86). This will end up lying outside the jited_len of the program, thus, when unwinding, we will fail to discover the return address as belonging to any program and end up in a panic due to the unreliable stack unwinding of BPF programs that we never expect. To remedy this case, make bpf_prog_ksym_find treat IP == ksym.end as part of the BPF program, so that is_bpf_text_address returns true when such a case occurs, and we are able to unwind reliably when the final instruction ends up being a call instruction. References: http://web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2023-52828 https://git.kernel.org/pub/scm/linux/security/vulns.git/plain/cve/published/2023/CVE-2023-52828.mbox https://git.kernel.org/stable/c/6058e4829696412457729a00734969acc6fd1d18 https://git.kernel.org/stable/c/cf353904a82873e952633fcac4385c2fcd3a46e1 https://git.kernel.org/stable/c/aa42a7cb92647786719fe9608685da345883878f https://git.kernel.org/stable/c/327b92e8cb527ae097961ffd1610c720481947f5 https://git.kernel.org/stable/c/821a7e4143af115b840ec199eb179537e18af922 https://git.kernel.org/stable/c/66d9111f3517f85ef2af0337ece02683ce0faf21 https://www.cve.org/CVERecord?id=CVE-2023-52828 https://bugzilla.redhat.com/show_bug.cgi?id=2282668
66d9111f3517 ("bpf: Detect IP == ksym.end as part of BPF program") is only needed when BPF exception is supported (through the bpf_throw kfunc), which actually belong to the same series[1]. Since we do not support BPF exception in our kernel yet, we are not affected. Reassigning back to security team. 1: https://lore.kernel.org/all/20230912233214.1518551-1-memxor@gmail.com/
(In reply to Shung-Hsi Yu from comment #3) > 66d9111f3517 ("bpf: Detect IP == ksym.end as part of BPF program") is only > needed when BPF exception is supported (through the bpf_throw kfunc), which > actually belong to the same series[1]. > > Since we do not support BPF exception in our kernel yet, we are not affected. > > Reassigning back to security team. > > 1: https://lore.kernel.org/all/20230912233214.1518551-1-memxor@gmail.com/ Thanks for the analysis. Closing