diff options
| author | Alexei Starovoitov <ast@kernel.org> | 2020-03-10 17:39:06 -0700 |
|---|---|---|
| committer | Daniel Borkmann <daniel@iogearbox.net> | 2020-03-11 14:07:32 +0100 |
| commit | 13fac1d851e09109096b5862bf37c3da6908fb48 (patch) | |
| tree | 927815f0128976e44e7f0435f52b91dd348ca4ea | |
| parent | babf3164095b0670435910340c2a1eec37757b57 (diff) | |
bpf: Fix trampoline generation for fmod_ret programs
fmod_ret progs are emitted as:
start = __bpf_prog_enter();
call fmod_ret
*(u64 *)(rbp - 8) = rax
__bpf_prog_exit(, start);
test eax, eax
jne do_fexit
That 'test eax, eax' is working by accident. The compiler is free to use rax
inside __bpf_prog_exit() or inside functions that __bpf_prog_exit() is calling.
Which caused "test_progs -t modify_return" to sporadically fail depending on
compiler version and kconfig. Fix it by using 'cmp [rbp - 8], 0' instead of
'test eax, eax'.
Fixes: ae24082331d9 ("bpf: Introduce BPF_MODIFY_RETURN")
Reported-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Acked-by: KP Singh <kpsingh@google.com>
Link: https://lore.kernel.org/bpf/20200311003906.3643037-1-ast@kernel.org
| -rw-r--r-- | arch/x86/net/bpf_jit_comp.c | 31 |
1 files changed, 5 insertions, 26 deletions
diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c index b1fd000feb89..5ea7c2cf7ab4 100644 --- a/arch/x86/net/bpf_jit_comp.c +++ b/arch/x86/net/bpf_jit_comp.c @@ -1449,23 +1449,6 @@ static int emit_cond_near_jump(u8 **pprog, void *func, void *ip, u8 jmp_cond) return 0; } -static int emit_mod_ret_check_imm8(u8 **pprog, int value) -{ - u8 *prog = *pprog; - int cnt = 0; - - if (!is_imm8(value)) - return -EINVAL; - - if (value == 0) - EMIT2(0x85, add_2reg(0xC0, BPF_REG_0, BPF_REG_0)); - else - EMIT3(0x83, add_1reg(0xF8, BPF_REG_0), value); - - *pprog = prog; - return 0; -} - static int invoke_bpf(const struct btf_func_model *m, u8 **pprog, struct bpf_tramp_progs *tp, int stack_size) { @@ -1485,7 +1468,7 @@ static int invoke_bpf_mod_ret(const struct btf_func_model *m, u8 **pprog, u8 **branches) { u8 *prog = *pprog; - int i; + int i, cnt = 0; /* The first fmod_ret program will receive a garbage return value. * Set this to 0 to avoid confusing the program. @@ -1496,16 +1479,12 @@ static int invoke_bpf_mod_ret(const struct btf_func_model *m, u8 **pprog, if (invoke_bpf_prog(m, &prog, tp->progs[i], stack_size, true)) return -EINVAL; - /* Generate a branch: - * - * if (ret != 0) + /* mod_ret prog stored return value into [rbp - 8]. Emit: + * if (*(u64 *)(rbp - 8) != 0) * goto do_fexit; - * - * If needed this can be extended to any integer value which can - * be passed by user-space when the program is loaded. */ - if (emit_mod_ret_check_imm8(&prog, 0)) - return -EINVAL; + /* cmp QWORD PTR [rbp - 0x8], 0x0 */ + EMIT4(0x48, 0x83, 0x7d, 0xf8); EMIT1(0x00); /* Save the location of the branch and Generate 6 nops * (4 bytes for an offset and 2 bytes for the jump) These nops |