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

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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: e54bcde3d6 ("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>
This commit is contained in:
Xi Wang 2015-06-25 05:47:39 -07:00 committed by Catalin Marinas
parent be081d9bf3
commit 8eee539dde
1 changed files with 4 additions and 3 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

7
arch/arm64/net/bpf_jit_comp.c
View file

@ -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, static inline int bpf2a64_offset(int bpf_to, int bpf_from,
const struct jit_ctx *ctx) 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 */ /* -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; return to - from;
} }
@ -640,10 +640,11 @@ static int build_body(struct jit_ctx *ctx)
const struct bpf_insn *insn = &prog->insnsi[i]; const struct bpf_insn *insn = &prog->insnsi[i];
int ret; int ret;
ret = build_insn(insn, ctx);
if (ctx->image == NULL) if (ctx->image == NULL)
ctx->offset[i] = ctx->idx; ctx->offset[i] = ctx->idx;
ret = build_insn(insn, ctx);
if (ret > 0) { if (ret > 0) {
i++; i++;
continue; continue;