From 484611357c19f9e19ef742ebef4505a07d243cc9 Mon Sep 17 00:00:00 2001 From: Josef Bacik Date: Wed, 28 Sep 2016 10:54:32 -0400 Subject: bpf: allow access into map value arrays Suppose you have a map array value that is something like this struct foo { unsigned iter; int array[SOME_CONSTANT]; }; You can easily insert this into an array, but you cannot modify the contents of foo->array[] after the fact. This is because we have no way to verify we won't go off the end of the array at verification time. This patch provides a start for this work. We accomplish this by keeping track of a minimum and maximum value a register could be while we're checking the code. Then at the time we try to do an access into a MAP_VALUE we verify that the maximum offset into that region is a valid access into that memory region. So in practice, code such as this unsigned index = 0; if (foo->iter >= SOME_CONSTANT) foo->iter = index; else index = foo->iter++; foo->array[index] = bar; would be allowed, as we can verify that index will always be between 0 and SOME_CONSTANT-1. If you wish to use signed values you'll have to have an extra check to make sure the index isn't less than 0, or do something like index %= SOME_CONSTANT. Signed-off-by: Josef Bacik Acked-by: Alexei Starovoitov Signed-off-by: David S. Miller --- samples/bpf/libbpf.h | 8 ++++++++ 1 file changed, 8 insertions(+) (limited to 'samples/bpf/libbpf.h') diff --git a/samples/bpf/libbpf.h b/samples/bpf/libbpf.h index 364582b77888..ac6edb61b64a 100644 --- a/samples/bpf/libbpf.h +++ b/samples/bpf/libbpf.h @@ -85,6 +85,14 @@ extern char bpf_log_buf[LOG_BUF_SIZE]; .off = 0, \ .imm = IMM }) +#define BPF_MOV32_IMM(DST, IMM) \ + ((struct bpf_insn) { \ + .code = BPF_ALU | BPF_MOV | BPF_K, \ + .dst_reg = DST, \ + .src_reg = 0, \ + .off = 0, \ + .imm = IMM }) + /* BPF_LD_IMM64 macro encodes single 'load 64-bit immediate' insn */ #define BPF_LD_IMM64(DST, IMM) \ BPF_LD_IMM64_RAW(DST, 0, IMM) -- cgit v1.2.3-55-g7522