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Message-Id: <20181204103727.568190251@linuxfoundation.org>
Date: Tue, 4 Dec 2018 11:48:25 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-kernel@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
stable@...r.kernel.org, Alexei Starovoitov <ast@...nel.org>,
Thomas Gleixner <tglx@...utronix.de>,
Ben Hutchings <ben.hutchings@...ethink.co.uk>,
Sasha Levin <sashal@...nel.org>
Subject: [PATCH 4.14 019/146] bpf: Prevent memory disambiguation attack
4.14-stable review patch. If anyone has any objections, please let me know.
------------------
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@...nel.org>
Signed-off-by: Thomas Gleixner <tglx@...utronix.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@...ethink.co.uk>
Signed-off-by: Sasha Levin <sashal@...nel.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;
--
2.17.1
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