On 5/8/20 11:53 PM, Alexei Starovoitov wrote:
From: Alexei Starovoitov <ast@xxxxxxxxxx>
Implement permissions as stated in uapi/linux/capability.h
In order to do that the verifier allow_ptr_leaks flag is split
into allow_ptr_leaks and bpf_capable flags and they are set as:
env->allow_ptr_leaks = perfmon_capable();
env->bpf_capable = bpf_capable();
bpf_capable enables bounded loops, variable stack access and other verifier features.
allow_ptr_leaks enable ptr leaks, ptr conversions, subtraction of pointers, etc.
It also disables side channel mitigations.
That means that the networking BPF program loaded with CAP_BPF + CAP_NET_ADMIN will
have speculative checks done by the verifier and other spectre mitigation applied.
Such networking BPF program will not be able to leak kernel pointers.
I don't quite follow this part in the code below yet, see my comments.
Signed-off-by: Alexei Starovoitov <ast@xxxxxxxxxx>
[...]
diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
index 6abd5a778fcd..c32a7880fa62 100644
--- a/include/linux/bpf_verifier.h
+++ b/include/linux/bpf_verifier.h
@@ -375,6 +375,7 @@ struct bpf_verifier_env {
u32 used_map_cnt; /* number of used maps */
u32 id_gen; /* used to generate unique reg IDs */
bool allow_ptr_leaks;
+ bool bpf_capable;
bool seen_direct_write;
struct bpf_insn_aux_data *insn_aux_data; /* array of per-insn state */
const struct bpf_line_info *prev_linfo;
diff --git a/kernel/bpf/arraymap.c b/kernel/bpf/arraymap.c
index 95d77770353c..264a9254dc39 100644
--- a/kernel/bpf/arraymap.c
+++ b/kernel/bpf/arraymap.c
@@ -77,7 +77,7 @@ static struct bpf_map *array_map_alloc(union bpf_attr *attr)
bool percpu = attr->map_type == BPF_MAP_TYPE_PERCPU_ARRAY;
int ret, numa_node = bpf_map_attr_numa_node(attr);
u32 elem_size, index_mask, max_entries;
- bool unpriv = !capable(CAP_SYS_ADMIN);
+ bool unpriv = !bpf_capable();
So here progs loaded with CAP_BPF will have spectre mitigations bypassed which
is the opposite of above statement, no?
u64 cost, array_size, mask64;
struct bpf_map_memory mem;
struct bpf_array *array;
[...]
diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index 6aa11de67315..8f421dd0c4cf 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -646,7 +646,7 @@ static bool bpf_prog_kallsyms_verify_off(const struct bpf_prog *fp)
void bpf_prog_kallsyms_add(struct bpf_prog *fp)
{
if (!bpf_prog_kallsyms_candidate(fp) ||
- !capable(CAP_SYS_ADMIN))
+ !bpf_capable())
return;
bpf_prog_ksym_set_addr(fp);
@@ -824,7 +824,7 @@ static int bpf_jit_charge_modmem(u32 pages)
{
if (atomic_long_add_return(pages, &bpf_jit_current) >
(bpf_jit_limit >> PAGE_SHIFT)) {
- if (!capable(CAP_SYS_ADMIN)) {
+ if (!bpf_capable()) {
Should there still be an upper charge on module mem for !CAP_SYS_ADMIN?
atomic_long_sub(pages, &bpf_jit_current);
return -EPERM;
}
[...]
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 70ad009577f8..a6893746cd87 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
[...]
@@ -3428,7 +3429,7 @@ static int check_stack_boundary(struct bpf_verifier_env *env, int regno,
* Spectre masking for stack ALU.
* See also retrieve_ptr_limit().
*/
- if (!env->allow_ptr_leaks) {
+ if (!env->bpf_capable) {
This needs to stay on env->allow_ptr_leaks, the can_skip_alu_sanitation() does
check on env->allow_ptr_leaks as well, otherwise this breaks spectre mitgation
when masking alu.
char tn_buf[48];
tnum_strn(tn_buf, sizeof(tn_buf), reg->var_off);
@@ -7229,7 +7230,7 @@ static int push_insn(int t, int w, int e, struct bpf_verifier_env *env,
insn_stack[env->cfg.cur_stack++] = w;
return 1;
} else if ((insn_state[w] & 0xF0) == DISCOVERED) {
- if (loop_ok && env->allow_ptr_leaks)
+ if (loop_ok && env->bpf_capable)
return 0;
verbose_linfo(env, t, "%d: ", t);
verbose_linfo(env, w, "%d: ", w);
@@ -8338,7 +8339,7 @@ static int is_state_visited(struct bpf_verifier_env *env, int insn_idx)
if (env->max_states_per_insn < states_cnt)
env->max_states_per_insn = states_cnt;
- if (!env->allow_ptr_leaks && states_cnt > BPF_COMPLEXITY_LIMIT_STATES)
+ if (!env->bpf_capable && states_cnt > BPF_COMPLEXITY_LIMIT_STATES)
return push_jmp_history(env, cur);
if (!add_new_state)
@@ -9998,7 +9999,7 @@ static int fixup_bpf_calls(struct bpf_verifier_env *env)
insn->code = BPF_JMP | BPF_TAIL_CALL;
aux = &env->insn_aux_data[i + delta];
- if (env->allow_ptr_leaks && !expect_blinding &&
+ if (env->bpf_capable && !expect_blinding &&
prog->jit_requested &&
!bpf_map_key_poisoned(aux) &&
!bpf_map_ptr_poisoned(aux) &&
@@ -10725,7 +10726,7 @@ int bpf_check(struct bpf_prog **prog, union bpf_attr *attr,
env->insn_aux_data[i].orig_idx = i;
env->prog = *prog;
env->ops = bpf_verifier_ops[env->prog->type];
- is_priv = capable(CAP_SYS_ADMIN);
+ is_priv = bpf_capable();
if (!btf_vmlinux && IS_ENABLED(CONFIG_DEBUG_INFO_BTF)) {
mutex_lock(&bpf_verifier_lock);
@@ -10766,7 +10767,8 @@ int bpf_check(struct bpf_prog **prog, union bpf_attr *attr,
if (attr->prog_flags & BPF_F_ANY_ALIGNMENT)
env->strict_alignment = false;
- env->allow_ptr_leaks = is_priv;
+ env->allow_ptr_leaks = perfmon_capable();
+ env->bpf_capable = bpf_capable();
