linux-kernel - [PATCH v3 3/4] bpf: Fix ORC unwinding in non-JIT BPF code

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Date:   Wed, 26 Jun 2019 19:33:54 -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>
Subject: [PATCH v3 3/4] 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
rename the variable to "jump_table" so objtool can recognize it.

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 | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index 080e2bb644cc..ff66294882f8 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 *jump_table[256] = {
 		[0 ... 255] = &&default_label,
 		/* Now overwrite non-defaults ... */
 		BPF_INSN_MAP(BPF_INSN_2_LBL, BPF_INSN_3_LBL),
@@ -1315,7 +1315,7 @@ static u64 ___bpf_prog_run(u64 *regs, const struct bpf_insn *insn, u64 *stack)
 #define CONT_JMP ({ insn++; goto select_insn; })
 
 select_insn:
-	goto *jumptable[insn->code];
+	goto *jump_table[insn->code];
 
 	/* ALU */
 #define ALU(OPCODE, OP)			\
@@ -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