Commit 8eee539d authored Jun 25, 2015 by Xi Wang Committed by Catalin Marinas Jun 25, 2015

arm64: bpf: fix out-of-bounds read in bpf2a64_offset()



Problems occur when bpf_to or bpf_from has value prog->len - 1 (e.g.,
"Very long jump backwards" in test_bpf where the last instruction is a
jump): since ctx->offset has length prog->len, ctx->offset[bpf_to + 1]
or ctx->offset[bpf_from + 1] will cause an out-of-bounds read, leading
to a bogus jump offset and kernel panic.

This patch moves updating ctx->offset to after calling build_insn(),
and changes indexing to use bpf_to and bpf_from without + 1.

Fixes: e54bcde3 ("arm64: eBPF JIT compiler")
Cc: <stable@vger.kernel.org> # 3.18+
Cc: Zi Shen Lim <zlim.lnx@gmail.com>
Cc: Will Deacon <will.deacon@arm.com>
Acked-by: Alexei Starovoitov <ast@plumgrid.com>
Signed-off-by: Xi Wang <xi.wang@gmail.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

parent be081d9b

arch/arm64/net/bpf_jit_comp.c

+4 −3

Original line number	Diff line number	Diff line
		@@ -113,9 +113,9 @@ static inline void emit_a64_mov_i(const int is64, const int reg,
		static inline int bpf2a64_offset(int bpf_to, int bpf_from,
		const struct jit_ctx *ctx)
		{
		int to = ctx->offset[bpf_to + 1];
		int to = ctx->offset[bpf_to];
		/* -1 to account for the Branch instruction */
		int from = ctx->offset[bpf_from + 1] - 1;
		int from = ctx->offset[bpf_from] - 1;

		return to - from;
		}
		@@ -640,10 +640,11 @@ static int build_body(struct jit_ctx *ctx)
		const struct bpf_insn *insn = &prog->insnsi[i];
		int ret;

		ret = build_insn(insn, ctx);

		if (ctx->image == NULL)
		ctx->offset[i] = ctx->idx;

		ret = build_insn(insn, ctx);
		if (ret > 0) {
		i++;
		continue;