linux-kernel - [PATCH v4 2/2] bpf: Fix ORC unwinding in non-JIT BPF code

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Date:   Thu, 27 Jun 2019 20:50:47 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     x86@...nel.org
Cc:     linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Song Liu <songliubraving@...com>,
        Kairui Song <kasong@...hat.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>, Ingo Molnar <mingo@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>
Subject: [PATCH v4 2/2] bpf: Fix ORC unwinding in non-JIT BPF code

Objtool previously ignored ___bpf_prog_run() because it didn't
understand the jump table.  This resulted in the ORC unwinder not being
able to unwind through non-JIT BPF code.

Now that objtool knows how to read jump tables, remove the whitelist and
annotate the jump table so objtool can recognize it.

Also add an additional "const" to the jump table definition to clarify
that the text pointers are constant.  Otherwise GCC sets the section
writable flag and the assembler spits out warnings.

Fixes: d15d356887e7 ("perf/x86: Make perf callchains work without CONFIG_FRAME_POINTER")
Reported-by: Song Liu <songliubraving@...com>
Signed-off-by: Josh Poimboeuf <jpoimboe@...hat.com>
---
 kernel/bpf/core.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index 7c473f208a10..45456a796d7f 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -1299,7 +1299,7 @@ static u64 ___bpf_prog_run(u64 *regs, const struct bpf_insn *insn, u64 *stack)
 {
 #define BPF_INSN_2_LBL(x, y)    [BPF_##x | BPF_##y] = &&x##_##y
 #define BPF_INSN_3_LBL(x, y, z) [BPF_##x | BPF_##y | BPF_##z] = &&x##_##y##_##z
-	static const void *jumptable[256] = {
+	static const void * const jumptable[256] __annotate_jump_table = {
 		[0 ... 255] = &&default_label,
 		/* Now overwrite non-defaults ... */
 		BPF_INSN_MAP(BPF_INSN_2_LBL, BPF_INSN_3_LBL),
@@ -1558,7 +1558,6 @@ static u64 ___bpf_prog_run(u64 *regs, const struct bpf_insn *insn, u64 *stack)
 		BUG_ON(1);
 		return 0;
 }
-STACK_FRAME_NON_STANDARD(___bpf_prog_run); /* jump table */
 
 #define PROG_NAME(stack_size) __bpf_prog_run##stack_size
 #define DEFINE_BPF_PROG_RUN(stack_size) \
-- 
2.20.1