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Merge branch 'reject-ptr-scalar-mix'

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Daniel Borkmann says:

====================
Follow-up fix to 979d63d50c ("bpf: prevent out of bounds speculation
on pointer arithmetic") in order to reject a corner case for sanitation
when ptr / scalars are mixed in the same alu op.
====================

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Alexei Starovoitov 2019-01-05 21:32:39 -08:00
commit 97274b6126
3 changed files with 169 additions and 13 deletions
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1
include/linux/bpf_verifier.h
View File

@ -172,6 +172,7 @@ struct bpf_verifier_state_list {
#define BPF_ALU_SANITIZE_SRC 1U
#define BPF_ALU_SANITIZE_DST 2U
#define BPF_ALU_NEG_VALUE (1U << 2)
#define BPF_ALU_NON_POINTER (1U << 3)
#define BPF_ALU_SANITIZE (BPF_ALU_SANITIZE_SRC | \
BPF_ALU_SANITIZE_DST)

61
kernel/bpf/verifier.c
View File

@ -3103,6 +3103,40 @@ static int retrieve_ptr_limit(const struct bpf_reg_state *ptr_reg,
}
}
static bool can_skip_alu_sanitation(const struct bpf_verifier_env *env,
const struct bpf_insn *insn)
{
return env->allow_ptr_leaks || BPF_SRC(insn->code) == BPF_K;
}
static int update_alu_sanitation_state(struct bpf_insn_aux_data *aux,
u32 alu_state, u32 alu_limit)
{
/* If we arrived here from different branches with different
* state or limits to sanitize, then this won't work.
*/
if (aux->alu_state &&
(aux->alu_state != alu_state ||
aux->alu_limit != alu_limit))
return -EACCES;
/* Corresponding fixup done in fixup_bpf_calls(). */
aux->alu_state = alu_state;
aux->alu_limit = alu_limit;
return 0;
}
static int sanitize_val_alu(struct bpf_verifier_env *env,
struct bpf_insn *insn)
{
struct bpf_insn_aux_data *aux = cur_aux(env);
if (can_skip_alu_sanitation(env, insn))
return 0;
return update_alu_sanitation_state(aux, BPF_ALU_NON_POINTER, 0);
}
static int sanitize_ptr_alu(struct bpf_verifier_env *env,
struct bpf_insn *insn,
const struct bpf_reg_state *ptr_reg,
@ -3117,7 +3151,7 @@ static int sanitize_ptr_alu(struct bpf_verifier_env *env,
struct bpf_reg_state tmp;
bool ret;
if (env->allow_ptr_leaks || BPF_SRC(insn->code) == BPF_K)
if (can_skip_alu_sanitation(env, insn))
return 0;
/* We already marked aux for masking from non-speculative
@ -3133,19 +3167,8 @@ static int sanitize_ptr_alu(struct bpf_verifier_env *env,
if (retrieve_ptr_limit(ptr_reg, &alu_limit, opcode, off_is_neg))
return 0;
/* If we arrived here from different branches with different
* limits to sanitize, then this won't work.
*/
if (aux->alu_state &&
(aux->alu_state != alu_state ||
aux->alu_limit != alu_limit))
if (update_alu_sanitation_state(aux, alu_state, alu_limit))
return -EACCES;
/* Corresponding fixup done in fixup_bpf_calls(). */
aux->alu_state = alu_state;
aux->alu_limit = alu_limit;
do_sim:
/* Simulate and find potential out-of-bounds access under
* speculative execution from truncation as a result of
@ -3418,6 +3441,8 @@ static int adjust_scalar_min_max_vals(struct bpf_verifier_env *env,
s64 smin_val, smax_val;
u64 umin_val, umax_val;
u64 insn_bitness = (BPF_CLASS(insn->code) == BPF_ALU64) ? 64 : 32;
u32 dst = insn->dst_reg;
int ret;
if (insn_bitness == 32) {
/* Relevant for 32-bit RSH: Information can propagate towards
@ -3452,6 +3477,11 @@ static int adjust_scalar_min_max_vals(struct bpf_verifier_env *env,
switch (opcode) {
case BPF_ADD:
ret = sanitize_val_alu(env, insn);
if (ret < 0) {
verbose(env, "R%d tried to add from different pointers or scalars\n", dst);
return ret;
}
if (signed_add_overflows(dst_reg->smin_value, smin_val) ||
signed_add_overflows(dst_reg->smax_value, smax_val)) {
dst_reg->smin_value = S64_MIN;
@ -3471,6 +3501,11 @@ static int adjust_scalar_min_max_vals(struct bpf_verifier_env *env,
dst_reg->var_off = tnum_add(dst_reg->var_off, src_reg.var_off);
break;
case BPF_SUB:
ret = sanitize_val_alu(env, insn);
if (ret < 0) {
verbose(env, "R%d tried to sub from different pointers or scalars\n", dst);
return ret;
}
if (signed_sub_overflows(dst_reg->smin_value, smax_val) ||
signed_sub_overflows(dst_reg->smax_value, smin_val)) {
/* Overflow possible, we know nothing */

120
tools/testing/selftests/bpf/test_verifier.c
View File

@ -6933,6 +6933,126 @@ static struct bpf_test tests[] = {
.result = ACCEPT,
.retval = 1,
},
{
"map access: mixing value pointer and scalar, 1",
.insns = {
// load map value pointer into r0 and r2
BPF_MOV64_IMM(BPF_REG_0, 1),
BPF_LD_MAP_FD(BPF_REG_ARG1, 0),
BPF_MOV64_REG(BPF_REG_ARG2, BPF_REG_FP),
BPF_ALU64_IMM(BPF_ADD, BPF_REG_ARG2, -16),
BPF_ST_MEM(BPF_DW, BPF_REG_FP, -16, 0),
BPF_EMIT_CALL(BPF_FUNC_map_lookup_elem),
BPF_JMP_IMM(BPF_JNE, BPF_REG_0, 0, 1),
BPF_EXIT_INSN(),
// load some number from the map into r1
BPF_LDX_MEM(BPF_B, BPF_REG_1, BPF_REG_0, 0),
// depending on r1, branch:
BPF_JMP_IMM(BPF_JNE, BPF_REG_1, 0, 3),
// branch A
BPF_MOV64_REG(BPF_REG_2, BPF_REG_0),
BPF_MOV64_IMM(BPF_REG_3, 0),
BPF_JMP_A(2),
// branch B
BPF_MOV64_IMM(BPF_REG_2, 0),
BPF_MOV64_IMM(BPF_REG_3, 0x100000),
// common instruction
BPF_ALU64_REG(BPF_ADD, BPF_REG_2, BPF_REG_3),
// depending on r1, branch:
BPF_JMP_IMM(BPF_JNE, BPF_REG_1, 0, 1),
// branch A
BPF_JMP_A(4),
// branch B
BPF_MOV64_IMM(BPF_REG_0, 0x13371337),
// verifier follows fall-through
BPF_JMP_IMM(BPF_JNE, BPF_REG_2, 0x100000, 2),
BPF_MOV64_IMM(BPF_REG_0, 0),
BPF_EXIT_INSN(),
// fake-dead code; targeted from branch A to
// prevent dead code sanitization
BPF_LDX_MEM(BPF_B, BPF_REG_0, BPF_REG_0, 0),
BPF_MOV64_IMM(BPF_REG_0, 0),
BPF_EXIT_INSN(),
},
.fixup_map_array_48b = { 1 },
.result = ACCEPT,
.result_unpriv = REJECT,
.errstr_unpriv = "R2 tried to add from different pointers or scalars",
.retval = 0,
},
{
"map access: mixing value pointer and scalar, 2",
.insns = {
// load map value pointer into r0 and r2
BPF_MOV64_IMM(BPF_REG_0, 1),
BPF_LD_MAP_FD(BPF_REG_ARG1, 0),
BPF_MOV64_REG(BPF_REG_ARG2, BPF_REG_FP),
BPF_ALU64_IMM(BPF_ADD, BPF_REG_ARG2, -16),
BPF_ST_MEM(BPF_DW, BPF_REG_FP, -16, 0),
BPF_EMIT_CALL(BPF_FUNC_map_lookup_elem),
BPF_JMP_IMM(BPF_JNE, BPF_REG_0, 0, 1),
BPF_EXIT_INSN(),
// load some number from the map into r1
BPF_LDX_MEM(BPF_B, BPF_REG_1, BPF_REG_0, 0),
// depending on r1, branch:
BPF_JMP_IMM(BPF_JEQ, BPF_REG_1, 0, 3),
// branch A
BPF_MOV64_IMM(BPF_REG_2, 0),
BPF_MOV64_IMM(BPF_REG_3, 0x100000),
BPF_JMP_A(2),
// branch B
BPF_MOV64_REG(BPF_REG_2, BPF_REG_0),
BPF_MOV64_IMM(BPF_REG_3, 0),
// common instruction
BPF_ALU64_REG(BPF_ADD, BPF_REG_2, BPF_REG_3),
// depending on r1, branch:
BPF_JMP_IMM(BPF_JNE, BPF_REG_1, 0, 1),
// branch A
BPF_JMP_A(4),
// branch B
BPF_MOV64_IMM(BPF_REG_0, 0x13371337),
// verifier follows fall-through
BPF_JMP_IMM(BPF_JNE, BPF_REG_2, 0x100000, 2),
BPF_MOV64_IMM(BPF_REG_0, 0),
BPF_EXIT_INSN(),
// fake-dead code; targeted from branch A to
// prevent dead code sanitization
BPF_LDX_MEM(BPF_B, BPF_REG_0, BPF_REG_0, 0),
BPF_MOV64_IMM(BPF_REG_0, 0),
BPF_EXIT_INSN(),
},
.fixup_map_array_48b = { 1 },
.result = ACCEPT,
.result_unpriv = REJECT,
.errstr_unpriv = "R2 tried to add from different maps or paths",
.retval = 0,
},
{
"sanitation: alu with different scalars",
.insns = {
BPF_MOV64_IMM(BPF_REG_0, 1),
BPF_LD_MAP_FD(BPF_REG_ARG1, 0),
BPF_MOV64_REG(BPF_REG_ARG2, BPF_REG_FP),
BPF_ALU64_IMM(BPF_ADD, BPF_REG_ARG2, -16),
BPF_ST_MEM(BPF_DW, BPF_REG_FP, -16, 0),
BPF_EMIT_CALL(BPF_FUNC_map_lookup_elem),
BPF_JMP_IMM(BPF_JNE, BPF_REG_0, 0, 1),
BPF_EXIT_INSN(),
BPF_LDX_MEM(BPF_B, BPF_REG_1, BPF_REG_0, 0),
BPF_JMP_IMM(BPF_JEQ, BPF_REG_1, 0, 3),
BPF_MOV64_IMM(BPF_REG_2, 0),
BPF_MOV64_IMM(BPF_REG_3, 0x100000),
BPF_JMP_A(2),
BPF_MOV64_IMM(BPF_REG_2, 42),
BPF_MOV64_IMM(BPF_REG_3, 0x100001),
BPF_ALU64_REG(BPF_ADD, BPF_REG_2, BPF_REG_3),
BPF_MOV64_REG(BPF_REG_0, BPF_REG_2),
BPF_EXIT_INSN(),
},
.fixup_map_array_48b = { 1 },
.result = ACCEPT,
.retval = 0x100000,
},
{
"map access: value_ptr += known scalar, upper oob arith, test 1",
.insns = {