Hi James,

On 08/09/2017 10:34 PM, Daniel Borkmann wrote:
On 08/09/2017 09:39 AM, James Hogan wrote:
[...]
time (but please consider looking at the other patch which is certainly
a more real issue).


Sorry for the delay, started looking into that and whether we
have some other options, I'll get back to you on this.

Could we solve this more generically (as in: originally intended) in
the sense that we don't need to trust the gcc va_list handling; I feel
this is relying on an implementation detail? Perhaps something like
below poc patch?

Thanks again,
Daniel

From 71f16544d455abb6bb82f7253c17c14d2a395e91 Mon Sep 17 00:00:00 2001
Message-Id: 
<71f16544d455abb6bb82f7253c17c14d2a395e91.1502469361.git.dan...@iogearbox.net>
From: Daniel Borkmann <dan...@iogearbox.net>
Date: Fri, 11 Aug 2017 15:56:32 +0200
Subject: [PATCH] bpf: fix bpf_trace_printk on 32 bit

Signed-off-by: Daniel Borkmann <dan...@iogearbox.net>
---
 kernel/trace/bpf_trace.c | 31 +++++++++++++++++++++++++++----
 1 file changed, 27 insertions(+), 4 deletions(-)

diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index 3738519..d4cb36f 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -204,10 +204,33 @@ static const struct bpf_func_proto 
*bpf_get_probe_write_proto(void)
                fmt_cnt++;
        }

-       return __trace_printk(1/* fake ip will not be printed */, fmt,
-                             mod[0] == 2 ? arg1 : mod[0] == 1 ? (long) arg1 : 
(u32) arg1,
-                             mod[1] == 2 ? arg2 : mod[1] == 1 ? (long) arg2 : 
(u32) arg2,
-                             mod[2] == 2 ? arg3 : mod[2] == 1 ? (long) arg3 : 
(u32) arg3);
+#define __BPF_TP_EMIT()        __BPF_ARG3_TP()
+#define __BPF_TP(...)                                                  \
+       __trace_printk(1 /* fake ip will not be printed */,             \
+                      fmt, ##__VA_ARGS__)
+
+#define __BPF_ARG1_TP(...)                                             \
+       ((mod[0] == 2 || (mod[0] == 1 && __BITS_PER_LONG == 64))        \
+         ? __BPF_TP(arg1, ##__VA_ARGS__)                               \
+         : ((mod[0] == 1 || (mod[0] == 0 && __BITS_PER_LONG == 32))    \
+             ? __BPF_TP((long)arg1, ##__VA_ARGS__)                     \
+             : __BPF_TP((u32)arg1, ##__VA_ARGS__)))
+
+#define __BPF_ARG2_TP(...)                                             \
+       ((mod[1] == 2 || (mod[1] == 1 && __BITS_PER_LONG == 64))        \
+         ? __BPF_ARG1_TP(arg2, ##__VA_ARGS__)                          \
+         : ((mod[1] == 1 || (mod[1] == 0 && __BITS_PER_LONG == 32))    \
+             ? __BPF_ARG1_TP((long)arg2, ##__VA_ARGS__)                \
+             : __BPF_ARG1_TP((u32)arg2, ##__VA_ARGS__)))
+
+#define __BPF_ARG3_TP(...)                                             \
+       ((mod[2] == 2 || (mod[2] == 1 && __BITS_PER_LONG == 64))        \
+         ? __BPF_ARG2_TP(arg3, ##__VA_ARGS__)                          \
+         : ((mod[2] == 1 || (mod[2] == 0 && __BITS_PER_LONG == 32))    \
+             ? __BPF_ARG2_TP((long)arg3, ##__VA_ARGS__)                \
+             : __BPF_ARG2_TP((u32)arg3, ##__VA_ARGS__)))
+
+       return __BPF_TP_EMIT();
 }

 static const struct bpf_func_proto bpf_trace_printk_proto = {
--
1.9.3

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