4.14-stable review patch. If anyone has any objections, please let me know.
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commit af86ca4e3088fe5eacf2f7e58c01fa68ca067672 upstream.
Detect code patterns where malicious 'speculative store bypass' can be used and sanitize such patterns.
39: (bf) r3 = r10 40: (07) r3 += -216 41: (79) r8 = *(u64 *)(r7 +0) // slow read 42: (7a) *(u64 *)(r10 -72) = 0 // verifier inserts this instruction 43: (7b) *(u64 *)(r8 +0) = r3 // this store becomes slow due to r8 44: (79) r1 = *(u64 *)(r6 +0) // cpu speculatively executes this load 45: (71) r2 = *(u8 *)(r1 +0) // speculatively arbitrary 'load byte' // is now sanitized
Above code after x86 JIT becomes: e5: mov %rbp,%rdx e8: add $0xffffffffffffff28,%rdx ef: mov 0x0(%r13),%r14 f3: movq $0x0,-0x48(%rbp) fb: mov %rdx,0x0(%r14) ff: mov 0x0(%rbx),%rdi 103: movzbq 0x0(%rdi),%rsi
Signed-off-by: Alexei Starovoitov ast@kernel.org Signed-off-by: Thomas Gleixner tglx@linutronix.de [bwh: Backported to 4.14: - Add bpf_verifier_env parameter to check_stack_write() - Look up stack slot_types with state->stack_slot_type[] rather than state->stack[].slot_type[] - Drop bpf_verifier_env argument to verbose() - Adjust context] Signed-off-by: Ben Hutchings ben.hutchings@codethink.co.uk Signed-off-by: Sasha Levin sashal@kernel.org --- include/linux/bpf_verifier.h | 1 + kernel/bpf/verifier.c | 62 +++++++++++++++++++++++++++++++++--- 2 files changed, 59 insertions(+), 4 deletions(-)
diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h index a3333004fd2b..8458cc5fbce5 100644 --- a/include/linux/bpf_verifier.h +++ b/include/linux/bpf_verifier.h @@ -113,6 +113,7 @@ struct bpf_insn_aux_data { struct bpf_map *map_ptr; /* pointer for call insn into lookup_elem */ }; int ctx_field_size; /* the ctx field size for load insn, maybe 0 */ + int sanitize_stack_off; /* stack slot to be cleared */ bool seen; /* this insn was processed by the verifier */ };
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 013b0cd1958e..f6755fd5bae2 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -717,8 +717,9 @@ static bool is_spillable_regtype(enum bpf_reg_type type) /* check_stack_read/write functions track spill/fill of registers, * stack boundary and alignment are checked in check_mem_access() */ -static int check_stack_write(struct bpf_verifier_state *state, int off, - int size, int value_regno) +static int check_stack_write(struct bpf_verifier_env *env, + struct bpf_verifier_state *state, int off, + int size, int value_regno, int insn_idx) { int i, spi = (MAX_BPF_STACK + off) / BPF_REG_SIZE; /* caller checked that off % size == 0 and -MAX_BPF_STACK <= off < 0, @@ -738,8 +739,32 @@ static int check_stack_write(struct bpf_verifier_state *state, int off, state->spilled_regs[spi] = state->regs[value_regno]; state->spilled_regs[spi].live |= REG_LIVE_WRITTEN;
- for (i = 0; i < BPF_REG_SIZE; i++) + for (i = 0; i < BPF_REG_SIZE; i++) { + if (state->stack_slot_type[MAX_BPF_STACK + off + i] == STACK_MISC && + !env->allow_ptr_leaks) { + int *poff = &env->insn_aux_data[insn_idx].sanitize_stack_off; + int soff = (-spi - 1) * BPF_REG_SIZE; + + /* detected reuse of integer stack slot with a pointer + * which means either llvm is reusing stack slot or + * an attacker is trying to exploit CVE-2018-3639 + * (speculative store bypass) + * Have to sanitize that slot with preemptive + * store of zero. + */ + if (*poff && *poff != soff) { + /* disallow programs where single insn stores + * into two different stack slots, since verifier + * cannot sanitize them + */ + verbose("insn %d cannot access two stack slots fp%d and fp%d", + insn_idx, *poff, soff); + return -EINVAL; + } + *poff = soff; + } state->stack_slot_type[MAX_BPF_STACK + off + i] = STACK_SPILL; + } } else { /* regular write of data into stack */ state->spilled_regs[spi] = (struct bpf_reg_state) {}; @@ -1216,7 +1241,8 @@ static int check_mem_access(struct bpf_verifier_env *env, int insn_idx, u32 regn verbose("attempt to corrupt spilled pointer on stack\n"); return -EACCES; } - err = check_stack_write(state, off, size, value_regno); + err = check_stack_write(env, state, off, size, + value_regno, insn_idx); } else { err = check_stack_read(state, off, size, value_regno); } @@ -4270,6 +4296,34 @@ static int convert_ctx_accesses(struct bpf_verifier_env *env) else continue;
+ if (type == BPF_WRITE && + env->insn_aux_data[i + delta].sanitize_stack_off) { + struct bpf_insn patch[] = { + /* Sanitize suspicious stack slot with zero. + * There are no memory dependencies for this store, + * since it's only using frame pointer and immediate + * constant of zero + */ + BPF_ST_MEM(BPF_DW, BPF_REG_FP, + env->insn_aux_data[i + delta].sanitize_stack_off, + 0), + /* the original STX instruction will immediately + * overwrite the same stack slot with appropriate value + */ + *insn, + }; + + cnt = ARRAY_SIZE(patch); + new_prog = bpf_patch_insn_data(env, i + delta, patch, cnt); + if (!new_prog) + return -ENOMEM; + + delta += cnt - 1; + env->prog = new_prog; + insn = new_prog->insnsi + i + delta; + continue; + } + if (env->insn_aux_data[i + delta].ptr_type != PTR_TO_CTX) continue;