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Merge branch 'variable-stack-access' 

Andrey Ignatov says:

====================
The patch set adds support for stack access with variable offset from helpers.

Patch 1 is the main patch in the set and provides more details.
Patch 2 adds selftests for new functionality.
====================

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Alexei Starovoitov 2019-03-29 12:05:36 -07:00
parent dd399ac9e3 8ff80e96e3
commit c3969de8ac
2 changed files with 131 additions and 23 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

75
kernel/bpf/verifier.c
View File

@ -2157,6 +2157,29 @@ static int check_xadd(struct bpf_verifier_env *env, int insn_idx, struct bpf_ins
BPF_SIZE(insn->code), BPF_WRITE, -1, true);
}
static int __check_stack_boundary(struct bpf_verifier_env *env, u32 regno,
int off, int access_size,
bool zero_size_allowed)
{
struct bpf_reg_state *reg = reg_state(env, regno);
if (off >= 0 || off < -MAX_BPF_STACK || off + access_size > 0 ||
access_size < 0 || (access_size == 0 && !zero_size_allowed)) {
if (tnum_is_const(reg->var_off)) {
verbose(env, "invalid stack type R%d off=%d access_size=%d\n",
regno, off, access_size);
} else {
char tn_buf[48];
tnum_strn(tn_buf, sizeof(tn_buf), reg->var_off);
verbose(env, "invalid stack type R%d var_off=%s access_size=%d\n",
regno, tn_buf, access_size);
}
return -EACCES;
}
return 0;
}
/* when register 'regno' is passed into function that will read 'access_size'
* bytes from that pointer, make sure that it's within stack boundary
* and all elements of stack are initialized.
@ -2169,7 +2192,7 @@ static int check_stack_boundary(struct bpf_verifier_env *env, int regno,
{
struct bpf_reg_state *reg = reg_state(env, regno);
struct bpf_func_state *state = func(env, reg);
int off, i, slot, spi;
int err, min_off, max_off, i, slot, spi;
if (reg->type != PTR_TO_STACK) {
/* Allow zero-byte read from NULL, regardless of pointer type */
@ -2183,21 +2206,23 @@ static int check_stack_boundary(struct bpf_verifier_env *env, int regno,
return -EACCES;
}
/* Only allow fixed-offset stack reads */
if (!tnum_is_const(reg->var_off)) {
char tn_buf[48];
tnum_strn(tn_buf, sizeof(tn_buf), reg->var_off);
verbose(env, "invalid variable stack read R%d var_off=%s\n",
regno, tn_buf);
return -EACCES;
}
off = reg->off + reg->var_off.value;
if (off >= 0 || off < -MAX_BPF_STACK || off + access_size > 0 ||
access_size < 0 || (access_size == 0 && !zero_size_allowed)) {
verbose(env, "invalid stack type R%d off=%d access_size=%d\n",
regno, off, access_size);
return -EACCES;
if (tnum_is_const(reg->var_off)) {
min_off = max_off = reg->var_off.value + reg->off;
err = __check_stack_boundary(env, regno, min_off, access_size,
zero_size_allowed);
if (err)
return err;
} else {
min_off = reg->smin_value + reg->off;
max_off = reg->umax_value + reg->off;
err = __check_stack_boundary(env, regno, min_off, access_size,
zero_size_allowed);
if (err)
return err;
err = __check_stack_boundary(env, regno, max_off, access_size,
zero_size_allowed);
if (err)
return err;
}
if (meta && meta->raw_mode) {
@ -2206,10 +2231,10 @@ static int check_stack_boundary(struct bpf_verifier_env *env, int regno,
return 0;
}
for (i = 0; i < access_size; i++) {
for (i = min_off; i < max_off + access_size; i++) {
u8 *stype;
slot = -(off + i) - 1;
slot = -i - 1;
spi = slot / BPF_REG_SIZE;
if (state->allocated_stack <= slot)
goto err;
@ -2222,8 +2247,16 @@ static int check_stack_boundary(struct bpf_verifier_env *env, int regno,
goto mark;
}
err:
verbose(env, "invalid indirect read from stack off %d+%d size %d\n",
off, i, access_size);
if (tnum_is_const(reg->var_off)) {
verbose(env, "invalid indirect read from stack off %d+%d size %d\n",
min_off, i - min_off, access_size);
} else {
char tn_buf[48];
tnum_strn(tn_buf, sizeof(tn_buf), reg->var_off);
verbose(env, "invalid indirect read from stack var_off %s+%d size %d\n",
tn_buf, i - min_off, access_size);
}
return -EACCES;
mark:
/* reading any byte out of 8-byte 'spill_slot' will cause
@ -2232,7 +2265,7 @@ static int check_stack_boundary(struct bpf_verifier_env *env, int regno,
mark_reg_read(env, &state->stack[spi].spilled_ptr,
state->stack[spi].spilled_ptr.parent);
}
return update_stack_depth(env, state, off);
return update_stack_depth(env, state, min_off);
}
static int check_helper_mem_access(struct bpf_verifier_env *env, int regno,

79
tools/testing/selftests/bpf/verifier/var_off.c
View File

@ -40,7 +40,7 @@
.prog_type = BPF_PROG_TYPE_LWT_IN,
},
{
"indirect variable-offset stack access",
"indirect variable-offset stack access, out of bound",
.insns = {
/* Fill the top 8 bytes of the stack */
BPF_ST_MEM(BPF_DW, BPF_REG_10, -8, 0),
@ -60,7 +60,82 @@
BPF_EXIT_INSN(),
},
.fixup_map_hash_8b = { 5 },
.errstr = "variable stack read R2",
.errstr = "invalid stack type R2 var_off",
.result = REJECT,
.prog_type = BPF_PROG_TYPE_LWT_IN,
},
{
"indirect variable-offset stack access, max_off+size > max_initialized",
.insns = {
/* Fill only the second from top 8 bytes of the stack. */
BPF_ST_MEM(BPF_DW, BPF_REG_10, -16, 0),
/* Get an unknown value. */
BPF_LDX_MEM(BPF_W, BPF_REG_2, BPF_REG_1, 0),
/* Make it small and 4-byte aligned. */
BPF_ALU64_IMM(BPF_AND, BPF_REG_2, 4),
BPF_ALU64_IMM(BPF_SUB, BPF_REG_2, 16),
/* Add it to fp. We now have either fp-12 or fp-16, but we don't know
* which. fp-12 size 8 is partially uninitialized stack.
*/
BPF_ALU64_REG(BPF_ADD, BPF_REG_2, BPF_REG_10),
/* Dereference it indirectly. */
BPF_LD_MAP_FD(BPF_REG_1, 0),
BPF_EMIT_CALL(BPF_FUNC_map_lookup_elem),
BPF_MOV64_IMM(BPF_REG_0, 0),
BPF_EXIT_INSN(),
},
.fixup_map_hash_8b = { 5 },
.errstr = "invalid indirect read from stack var_off",
.result = REJECT,
.prog_type = BPF_PROG_TYPE_LWT_IN,
},
{
"indirect variable-offset stack access, min_off < min_initialized",
.insns = {
/* Fill only the top 8 bytes of the stack. */
BPF_ST_MEM(BPF_DW, BPF_REG_10, -8, 0),
/* Get an unknown value */
BPF_LDX_MEM(BPF_W, BPF_REG_2, BPF_REG_1, 0),
/* Make it small and 4-byte aligned. */
BPF_ALU64_IMM(BPF_AND, BPF_REG_2, 4),
BPF_ALU64_IMM(BPF_SUB, BPF_REG_2, 16),
/* Add it to fp. We now have either fp-12 or fp-16, but we don't know
* which. fp-16 size 8 is partially uninitialized stack.
*/
BPF_ALU64_REG(BPF_ADD, BPF_REG_2, BPF_REG_10),
/* Dereference it indirectly. */
BPF_LD_MAP_FD(BPF_REG_1, 0),
BPF_EMIT_CALL(BPF_FUNC_map_lookup_elem),
BPF_MOV64_IMM(BPF_REG_0, 0),
BPF_EXIT_INSN(),
},
.fixup_map_hash_8b = { 5 },
.errstr = "invalid indirect read from stack var_off",
.result = REJECT,
.prog_type = BPF_PROG_TYPE_LWT_IN,
},
{
"indirect variable-offset stack access, ok",
.insns = {
/* Fill the top 16 bytes of the stack. */
BPF_ST_MEM(BPF_DW, BPF_REG_10, -16, 0),
BPF_ST_MEM(BPF_DW, BPF_REG_10, -8, 0),
/* Get an unknown value. */
BPF_LDX_MEM(BPF_W, BPF_REG_2, BPF_REG_1, 0),
/* Make it small and 4-byte aligned. */
BPF_ALU64_IMM(BPF_AND, BPF_REG_2, 4),
BPF_ALU64_IMM(BPF_SUB, BPF_REG_2, 16),
/* Add it to fp. We now have either fp-12 or fp-16, we don't know
* which, but either way it points to initialized stack.
*/
BPF_ALU64_REG(BPF_ADD, BPF_REG_2, BPF_REG_10),
/* Dereference it indirectly. */
BPF_LD_MAP_FD(BPF_REG_1, 0),
BPF_EMIT_CALL(BPF_FUNC_map_lookup_elem),
BPF_MOV64_IMM(BPF_REG_0, 0),
BPF_EXIT_INSN(),
},
.fixup_map_hash_8b = { 6 },
.result = ACCEPT,
.prog_type = BPF_PROG_TYPE_LWT_IN,
},