lkml.org 
[lkml]   [2016]   [Feb]   [25]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH v18 4/9] bpf: Mark __bpf_prog_run() stack frame as non-standard
Date
objtool reports the following false positive warnings:

objtool: kernel/bpf/core.o: __bpf_prog_run()+0x5c: sibling call from callable instruction with changed frame pointer
objtool: kernel/bpf/core.o: __bpf_prog_run()+0x60: function has unreachable instruction
objtool: kernel/bpf/core.o: __bpf_prog_run()+0x64: function has unreachable instruction
[...]

It's confused by the following dynamic jump instruction in
__bpf_prog_run()::

jmp *(%r12,%rax,8)

which corresponds to the following line in the C code:

goto *jumptable[insn->code];

There's no way for objtool to deterministically find all possible
branch targets for a dynamic jump, so it can't verify this code.

In this case the jumps all stay within the function, and there's nothing
unusual going on related to the stack, so we can whitelist the function.

Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Cc: netdev@vger.kernel.org
---
kernel/bpf/core.c | 2 ++
1 file changed, 2 insertions(+)

diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index 972d9a8..be0abf6 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -27,6 +27,7 @@
#include <linux/random.h>
#include <linux/moduleloader.h>
#include <linux/bpf.h>
+#include <linux/frame.h>

#include <asm/unaligned.h>

@@ -649,6 +650,7 @@ load_byte:
WARN_RATELIMIT(1, "unknown opcode %02x\n", insn->code);
return 0;
}
+STACK_FRAME_NON_STANDARD(__bpf_prog_run); /* jump table */

bool bpf_prog_array_compatible(struct bpf_array *array,
const struct bpf_prog *fp)
--
2.4.3
\
 
 \ /
  Last update: 2016-02-26 00:41    [W:0.116 / U:0.200 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site