Netdev Archive on lore.kernel.org
 help / color / Atom feed
From: Josh Poimboeuf <jpoimboe@redhat.com>
To: x86@kernel.org, Alexei Starovoitov <ast@kernel.org>
Cc: linux-kernel@vger.kernel.org,
	Daniel Borkmann <daniel@iogearbox.net>,
	netdev@vger.kernel.org, bpf@vger.kernel.org,
	Peter Zijlstra <peterz@infradead.org>,
	Song Liu <songliubraving@fb.com>, Kairui Song <kasong@redhat.com>,
	Steven Rostedt <rostedt@goodmis.org>,
	David Laight <David.Laight@ACULAB.COM>,
	Thomas Gleixner <tglx@linutronix.de>,
	Borislav Petkov <bp@alien8.de>, Ingo Molnar <mingo@kernel.org>
Subject: [PATCH v2 2/5] objtool: Fix ORC unwinding in non-JIT BPF generated code
Date: Fri, 14 Jun 2019 12:56:41 -0500
Message-ID: <c0add777a2e0207c1474ce99baa492a7ce3502d6.1560534694.git.jpoimboe@redhat.com> (raw)
In-Reply-To: <cover.1560534694.git.jpoimboe@redhat.com>

Objtool currently ignores ___bpf_prog_run() because it doesn't
understand the jump table.  This results in the ORC unwinder not being
able to unwind through non-JIT BPF code.

Luckily, the BPF jump table resembles a GCC switch jump table, which
objtool already knows how to read.

Add generic support for reading any static local jump table array named
"jump_table", and rename the BPF variable accordingly, so objtool can
generate ORC data for ___bpf_prog_run().

Fixes: d15d356887e7 ("perf/x86: Make perf callchains work without CONFIG_FRAME_POINTER")
Reported-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
 kernel/bpf/core.c     |  5 ++---
 tools/objtool/check.c | 16 ++++++++++++++--
 2 files changed, 16 insertions(+), 5 deletions(-)

diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index 7c473f208a10..aa546ef7dbdc 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) \
diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 172f99195726..8341c2fff14f 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -18,6 +18,8 @@
 
 #define FAKE_JUMP_OFFSET -1
 
+#define JUMP_TABLE_SYM_PREFIX "jump_table."
+
 struct alternative {
 	struct list_head list;
 	struct instruction *insn;
@@ -997,6 +999,7 @@ static struct rela *find_switch_table(struct objtool_file *file,
 	struct instruction *orig_insn = insn;
 	struct section *rodata_sec;
 	unsigned long table_offset;
+	struct symbol *sym;
 
 	/*
 	 * Backward search using the @first_jump_src links, these help avoid
@@ -1035,9 +1038,18 @@ static struct rela *find_switch_table(struct objtool_file *file,
 
 		/*
 		 * Make sure the .rodata address isn't associated with a
-		 * symbol.  gcc jump tables are anonymous data.
+		 * symbol.  GCC jump tables are anonymous data.
+		 *
+		 * Also support C jump tables which are in the same format as
+		 * switch jump tables.  Each jump table should be a static
+		 * local const array named "jump_table" for objtool to
+		 * recognize it.  Note: GCC will add a numbered suffix to the
+		 * ELF symbol name, like "jump_table.12345", which it does for
+		 * all static local variables.
 		 */
-		if (find_symbol_containing(rodata_sec, table_offset))
+		sym = find_symbol_containing(rodata_sec, table_offset);
+		if (sym && strncmp(sym->name, JUMP_TABLE_SYM_PREFIX,
+				   strlen(JUMP_TABLE_SYM_PREFIX)))
 			continue;
 
 		rodata_rela = find_rela_by_dest(rodata_sec, table_offset);
-- 
2.20.1


  parent reply index

Thread overview: 31+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-06-14 17:56 [PATCH v2 0/5] x86/bpf: unwinder fixes Josh Poimboeuf
2019-06-14 17:56 ` [PATCH v2 1/5] perf/x86: Always store regs->ip in perf_callchain_kernel() Josh Poimboeuf
2019-06-14 20:56   ` Alexei Starovoitov
2019-06-14 21:06     ` Josh Poimboeuf
2019-06-14 21:16       ` Steven Rostedt
2019-06-14 21:20         ` Song Liu
2019-06-14 17:56 ` Josh Poimboeuf [this message]
2019-06-14 20:58   ` [PATCH v2 2/5] objtool: Fix ORC unwinding in non-JIT BPF generated code Alexei Starovoitov
2019-06-14 21:07     ` Josh Poimboeuf
2019-06-14 21:09       ` Alexei Starovoitov
2019-06-14 21:19         ` Josh Poimboeuf
2019-06-14 21:22           ` Alexei Starovoitov
2019-06-14 23:17             ` Josh Poimboeuf
2019-06-14 23:30               ` Alexei Starovoitov
2019-06-15  0:02                 ` Josh Poimboeuf
2019-06-15  0:06                   ` abhja kaanlani
2019-06-15  0:07                   ` Alexei Starovoitov
2019-06-17 14:57     ` David Laight
2019-06-14 17:56 ` [PATCH v2 3/5] x86/bpf: Move epilogue generation to a dedicated function Josh Poimboeuf
2019-06-14 17:56 ` [PATCH v2 4/5] x86/bpf: Fix 64-bit JIT frame pointer usage Josh Poimboeuf
2019-06-14 21:05   ` Alexei Starovoitov
2019-06-14 21:19     ` Josh Poimboeuf
2019-06-14 21:27       ` Alexei Starovoitov
2019-06-14 23:13         ` Josh Poimboeuf
2019-06-14 23:23           ` Alexei Starovoitov
2019-06-14 23:54             ` Josh Poimboeuf
2019-06-15  0:02               ` Alexei Starovoitov
2019-06-15  4:27                 ` Josh Poimboeuf
2019-06-15  5:16                   ` Alexei Starovoitov
2019-06-15 12:57                     ` Josh Poimboeuf
2019-06-14 17:56 ` [PATCH v2 5/5] x86/unwind/orc: Fall back to using frame pointers for generated code Josh Poimboeuf

Reply instructions:

You may reply publically to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=c0add777a2e0207c1474ce99baa492a7ce3502d6.1560534694.git.jpoimboe@redhat.com \
    --to=jpoimboe@redhat.com \
    --cc=David.Laight@ACULAB.COM \
    --cc=ast@kernel.org \
    --cc=bp@alien8.de \
    --cc=bpf@vger.kernel.org \
    --cc=daniel@iogearbox.net \
    --cc=kasong@redhat.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=mingo@kernel.org \
    --cc=netdev@vger.kernel.org \
    --cc=peterz@infradead.org \
    --cc=rostedt@goodmis.org \
    --cc=songliubraving@fb.com \
    --cc=tglx@linutronix.de \
    --cc=x86@kernel.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

Netdev Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/netdev/0 netdev/git/0.git
	git clone --mirror https://lore.kernel.org/netdev/1 netdev/git/1.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 netdev netdev/ https://lore.kernel.org/netdev \
		netdev@vger.kernel.org netdev@archiver.kernel.org
	public-inbox-index netdev


Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.netdev


AGPL code for this site: git clone https://public-inbox.org/ public-inbox