Uprobe programs that modify regs require different runtime assumptions than those that do not. Mixing !kprobe_write_ctx progs with kprobe_write_ctx progs via tail calls could break these assumptions. To address this, reject the combination of !kprobe_write_ctx progs with kprobe_write_ctx progs in bpf_map_owner_matches(), which prevents the tail callee from modifying regs unexpectedly. Also reject kprobe_write_ctx mismatches during initialization to prevent bypassing the above restriction. Without this check, the above restriction can be bypassed as follows. struct { __uint(type, BPF_MAP_TYPE_PROG_ARRAY); __uint(max_entries, 1); __uint(key_size, 4); __uint(value_size, 4); } jmp_table SEC(".maps"); SEC("?kprobe") int prog_a(struct pt_regs *regs) { regs->ax = 0; bpf_tail_call_static(regs, &jmp_table, 0); return 0; } SEC("?kprobe") int prog_b(struct pt_regs *regs) { bpf_tail_call_static(regs, &jmp_table, 0); return 0; } The jmp_table is shared between prog_a and prog_b. * Load prog_a. At this point, owner->kprobe_write_ctx=true. * Load prog_b. At this point, prog_b passes the compatibility check. * Add prog_a to jmp_table. * Attach prog_b to a kernel function. When the kernel function runs, prog_a will unexpectedly modify regs. Fixes: 7384893d970e ("bpf: Allow uprobe program to change context registers") Signed-off-by: Leon Hwang --- include/linux/bpf.h | 7 ++++--- kernel/bpf/core.c | 30 +++++++++++++++++++++++++----- 2 files changed, 29 insertions(+), 8 deletions(-) diff --git a/include/linux/bpf.h b/include/linux/bpf.h index 05b34a6355b0..dbafed52b2ba 100644 --- a/include/linux/bpf.h +++ b/include/linux/bpf.h @@ -285,9 +285,10 @@ struct bpf_list_node_kern { */ struct bpf_map_owner { enum bpf_prog_type type; - bool jited; - bool xdp_has_frags; - bool sleepable; + u32 jited:1; + u32 xdp_has_frags:1; + u32 sleepable:1; + u32 kprobe_write_ctx:1; u64 storage_cookie[MAX_BPF_CGROUP_STORAGE_TYPE]; const struct btf_type *attach_func_proto; enum bpf_attach_type expected_attach_type; diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c index b24a613d99f2..121a697d4da5 100644 --- a/kernel/bpf/core.c +++ b/kernel/bpf/core.c @@ -2390,6 +2390,7 @@ static void bpf_map_owner_init(struct bpf_map_owner *owner, const struct bpf_pro owner->jited = fp->jited; owner->xdp_has_frags = aux->xdp_has_frags; owner->sleepable = fp->sleepable; + owner->kprobe_write_ctx = aux->kprobe_write_ctx; owner->expected_attach_type = fp->expected_attach_type; owner->attach_func_proto = aux->attach_func_proto; for_each_cgroup_storage_type(i) @@ -2397,8 +2398,14 @@ static void bpf_map_owner_init(struct bpf_map_owner *owner, const struct bpf_pro aux->cgroup_storage[i]->cookie : 0; } +enum bpf_map_owner_match_type { + BPF_MAP_OWNER_MATCH_FOR_INIT, + BPF_MAP_OWNER_MATCH_FOR_UPDATE, +}; + static bool bpf_map_owner_matches(const struct bpf_map *map, const struct bpf_prog *fp, - enum bpf_prog_type prog_type) + enum bpf_prog_type prog_type, + enum bpf_map_owner_match_type match) { struct bpf_map_owner *owner = map->owner; struct bpf_prog_aux *aux = fp->aux; @@ -2411,6 +2418,18 @@ static bool bpf_map_owner_matches(const struct bpf_map *map, const struct bpf_pr owner->sleepable != fp->sleepable) return false; + switch (match) { + case BPF_MAP_OWNER_MATCH_FOR_INIT: + if (owner->kprobe_write_ctx != aux->kprobe_write_ctx) + return false; + break; + + case BPF_MAP_OWNER_MATCH_FOR_UPDATE: + if (!owner->kprobe_write_ctx && aux->kprobe_write_ctx) + return false; + break; + } + if (map->map_type == BPF_MAP_TYPE_PROG_ARRAY && owner->expected_attach_type != fp->expected_attach_type) return false; @@ -2436,7 +2455,8 @@ static bool bpf_map_owner_matches(const struct bpf_map *map, const struct bpf_pr } static bool __bpf_prog_map_compatible(struct bpf_map *map, - const struct bpf_prog *fp) + const struct bpf_prog *fp, + enum bpf_map_owner_match_type match) { enum bpf_prog_type prog_type = resolve_prog_type(fp); bool ret = false; @@ -2453,7 +2473,7 @@ static bool __bpf_prog_map_compatible(struct bpf_map *map, bpf_map_owner_init(map->owner, fp, prog_type); ret = true; } else { - ret = bpf_map_owner_matches(map, fp, prog_type); + ret = bpf_map_owner_matches(map, fp, prog_type, match); } err: spin_unlock(&map->owner_lock); @@ -2470,7 +2490,7 @@ bool bpf_prog_map_compatible(struct bpf_map *map, const struct bpf_prog *fp) if (bpf_prog_is_dev_bound(fp->aux)) return false; - return __bpf_prog_map_compatible(map, fp); + return __bpf_prog_map_compatible(map, fp, BPF_MAP_OWNER_MATCH_FOR_UPDATE); } static int bpf_check_tail_call(const struct bpf_prog *fp) @@ -2485,7 +2505,7 @@ static int bpf_check_tail_call(const struct bpf_prog *fp) if (!map_type_contains_progs(map)) continue; - if (!__bpf_prog_map_compatible(map, fp)) { + if (!__bpf_prog_map_compatible(map, fp, BPF_MAP_OWNER_MATCH_FOR_INIT)) { ret = -EINVAL; goto out; } -- 2.52.0