From: Peter Zijlstra <peterz@infradead.org>
To: peterz@infradead.org
Cc: paul.walmsley@sifive.com, palmer@dabbelt.com,
aou@eecs.berkeley.edu, tglx@linutronix.de, mingo@redhat.com,
bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org,
hpa@zytor.com, davem@davemloft.net, dsahern@kernel.org,
ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org,
martin.lau@linux.dev, song@kernel.org, yonghong.song@linux.dev,
john.fastabend@gmail.com, kpsingh@kernel.org, sdf@google.com,
haoluo@google.com, jolsa@kernel.org,
Arnd Bergmann <arnd@arndb.de>,
samitolvanen@google.com, keescook@chromium.org,
nathan@kernel.org, ndesaulniers@google.com,
linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org,
netdev@vger.kernel.org, bpf@vger.kernel.org,
linux-arch@vger.kernel.org, llvm@lists.linux.dev,
jpoimboe@kernel.org, joao@overdrivepizza.com,
mark.rutland@arm.com
Subject: [PATCH 0/2] x86/bpf: Fix FineIBT vs eBPF
Date: Mon, 20 Nov 2023 15:46:42 +0100 [thread overview]
Message-ID: <20231120144642.591358648@infradead.org> (raw)
Hi!
There's a problem with FineIBT and eBPF using __nocfi when
CONFIG_BPF_JIT_ALWAYS_ON=n, in which case the __nocfi indirect call can target
a normal function like __bpf_prog_run32().
Specifically the various preambles look like:
FineIBT JIT
__cfi_foo:
endbr64
subl $hash, %r10d
jz 1f
ud2
1: nop
foo: foo:
osp nop3 endbr64
... ...
So while bpf_dispatcher_*_func() does a __nocfi call to foo()+0 and this
matches what the JIT generates, it does not work for regular FineIBT functions,
since their +0 endbr got poisoned and things go *boom*.
Cure this by teaching the BPF JIT about all the various CFI forms. Notably this
removes the last __nocfi call on x86.
If the BPF folks agree (and the robots don't find fail) I'd like to take this
through the x86 tree, because I have a few more patches that turn the non-fatal
'osp nop3' poison into a 4 byte ud1 instruction which is rather fatal. As a
result this problem will also surface on !IBT hardware.
next reply other threads:[~2023-11-20 15:52 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-11-20 14:46 Peter Zijlstra [this message]
2023-11-20 14:46 ` [PATCH 1/2] cfi: Flip headers Peter Zijlstra
2023-11-20 14:46 ` [PATCH 2/2] x86/cfi,bpf: Fix BPF JIT call Peter Zijlstra
2023-11-20 15:59 ` Peter Zijlstra
2023-11-22 2:18 ` Alexei Starovoitov
2023-11-22 11:15 ` Peter Zijlstra
2023-11-22 12:41 ` Peter Zijlstra
2023-11-22 12:54 ` Peter Zijlstra
2023-11-23 0:51 ` Alexei Starovoitov
2023-11-23 0:43 ` Alexei Starovoitov
2023-12-01 23:54 ` Sami Tolvanen
2023-12-04 16:28 ` Nick Desaulniers
2023-11-22 1:41 ` [PATCH 0/2] x86/bpf: Fix FineIBT vs eBPF Alexei Starovoitov
2023-11-22 10:17 ` Peter Zijlstra
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