From 24b4d2abd0bd628f396dada3e915d395cbf459eb Mon Sep 17 00:00:00 2001 From: Alex Gartrell Date: Thu, 23 Jul 2015 14:24:40 -0700 Subject: [PATCH] ebpf: Allow dereferences of PTR_TO_STACK registers mov %rsp, %r1 ; r1 = rsp add $-8, %r1 ; r1 = rsp - 8 store_q $123, -8(%rsp) ; *(u64*)r1 = 123 <- valid store_q $123, (%r1) ; *(u64*)r1 = 123 <- previously invalid mov $0, %r0 exit ; Always need to exit And we'd get the following error: 0: (bf) r1 = r10 1: (07) r1 += -8 2: (7a) *(u64 *)(r10 -8) = 999 3: (7a) *(u64 *)(r1 +0) = 999 R1 invalid mem access 'fp' Unable to load program We already know that a register is a stack address and the appropriate offset, so we should be able to validate those references as well. Signed-off-by: Alex Gartrell Acked-by: Alexei Starovoitov Signed-off-by: David S. Miller --- kernel/bpf/verifier.c | 6 +++- samples/bpf/test_verifier.c | 59 +++++++++++++++++++++++++++++++++++++ 2 files changed, 64 insertions(+), 1 deletion(-) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 039d866fd36a..cd307df98cb3 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -648,6 +648,9 @@ static int check_mem_access(struct verifier_env *env, u32 regno, int off, struct verifier_state *state = &env->cur_state; int size, err = 0; + if (state->regs[regno].type == PTR_TO_STACK) + off += state->regs[regno].imm; + size = bpf_size_to_bytes(bpf_size); if (size < 0) return size; @@ -667,7 +670,8 @@ static int check_mem_access(struct verifier_env *env, u32 regno, int off, if (!err && t == BPF_READ && value_regno >= 0) mark_reg_unknown_value(state->regs, value_regno); - } else if (state->regs[regno].type == FRAME_PTR) { + } else if (state->regs[regno].type == FRAME_PTR || + state->regs[regno].type == PTR_TO_STACK) { if (off >= 0 || off < -MAX_BPF_STACK) { verbose("invalid stack off=%d size=%d\n", off, size); return -EACCES; diff --git a/samples/bpf/test_verifier.c b/samples/bpf/test_verifier.c index 693605997abc..ee0f110c9c54 100644 --- a/samples/bpf/test_verifier.c +++ b/samples/bpf/test_verifier.c @@ -822,6 +822,65 @@ static struct bpf_test tests[] = { .result = ACCEPT, .prog_type = BPF_PROG_TYPE_SCHED_CLS, }, + { + "PTR_TO_STACK store/load", + .insns = { + BPF_MOV64_REG(BPF_REG_1, BPF_REG_10), + BPF_ALU64_IMM(BPF_ADD, BPF_REG_1, -10), + BPF_ST_MEM(BPF_DW, BPF_REG_1, 2, 0xfaceb00c), + BPF_LDX_MEM(BPF_DW, BPF_REG_0, BPF_REG_1, 2), + BPF_EXIT_INSN(), + }, + .result = ACCEPT, + }, + { + "PTR_TO_STACK store/load - bad alignment on off", + .insns = { + BPF_MOV64_REG(BPF_REG_1, BPF_REG_10), + BPF_ALU64_IMM(BPF_ADD, BPF_REG_1, -8), + BPF_ST_MEM(BPF_DW, BPF_REG_1, 2, 0xfaceb00c), + BPF_LDX_MEM(BPF_DW, BPF_REG_0, BPF_REG_1, 2), + BPF_EXIT_INSN(), + }, + .result = REJECT, + .errstr = "misaligned access off -6 size 8", + }, + { + "PTR_TO_STACK store/load - bad alignment on reg", + .insns = { + BPF_MOV64_REG(BPF_REG_1, BPF_REG_10), + BPF_ALU64_IMM(BPF_ADD, BPF_REG_1, -10), + BPF_ST_MEM(BPF_DW, BPF_REG_1, 8, 0xfaceb00c), + BPF_LDX_MEM(BPF_DW, BPF_REG_0, BPF_REG_1, 8), + BPF_EXIT_INSN(), + }, + .result = REJECT, + .errstr = "misaligned access off -2 size 8", + }, + { + "PTR_TO_STACK store/load - out of bounds low", + .insns = { + BPF_MOV64_REG(BPF_REG_1, BPF_REG_10), + BPF_ALU64_IMM(BPF_ADD, BPF_REG_1, -80000), + BPF_ST_MEM(BPF_DW, BPF_REG_1, 8, 0xfaceb00c), + BPF_LDX_MEM(BPF_DW, BPF_REG_0, BPF_REG_1, 8), + BPF_EXIT_INSN(), + }, + .result = REJECT, + .errstr = "invalid stack off=-79992 size=8", + }, + { + "PTR_TO_STACK store/load - out of bounds high", + .insns = { + BPF_MOV64_REG(BPF_REG_1, BPF_REG_10), + BPF_ALU64_IMM(BPF_ADD, BPF_REG_1, -8), + BPF_ST_MEM(BPF_DW, BPF_REG_1, 8, 0xfaceb00c), + BPF_LDX_MEM(BPF_DW, BPF_REG_0, BPF_REG_1, 8), + BPF_EXIT_INSN(), + }, + .result = REJECT, + .errstr = "invalid stack off=0 size=8", + }, }; static int probe_filter_length(struct bpf_insn *fp) -- 2.30.2