bpf: fix bpf_trace_printk on 32 bit archs (88a5c690) · Commits · 戴 / test

James reported that on MIPS32 bpf_trace_printk() is currently broken while MIPS64 works fine: bpf_trace_printk() uses conditional operators to attempt to pass different types to __trace_printk() depending on the format operators. This doesn't work as intended on 32-bit architectures where u32 and long are passed differently to u64, since the result of C conditional operators follows the "usual arithmetic conversions" rules, such that the values passed to __trace_printk() will always be u64 [causing issues later in the va_list handling for vscnprintf()]. For example the samples/bpf/tracex5 test printed lines like below on MIPS32, where the fd and buf have come from the u64 fd argument, and the size from the buf argument: [...] 1180.941542: 0x00000001: write(fd=1, buf= (null), size=6258688) Instead of this: [...] 1625.616026: 0x00000001: write(fd=1, buf=009e4000, size=512) One way to get it working is to expand various combinations of argument types into 8 different combinations for 32 bit and 64 bit kernels. Fix tested by James on MIPS32 and MIPS64 as well that it resolves the issue. Fixes: ("tracing: Allow BPF programs to call bpf_trace_printk()") Reported-by:

James Hogan <james.hogan@imgtec.com> Tested-by:

James Hogan <james.hogan@imgtec.com> Signed-off-by:

Daniel Borkmann <daniel@iogearbox.net> Signed-off-by:

David S. Miller <davem@davemloft.net>

kernel/trace/bpf_trace.c

+30 −4

Original line number	Diff line number	Diff line
		@@ -204,10 +204,36 @@ BPF_CALL_5(bpf_trace_printk, char *, fmt, u32, fmt_size, u64, arg1,
		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);
		/* Horrid workaround for getting va_list handling working with different
		* argument type combinations generically for 32 and 64 bit archs.
		*/
		#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 = {

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