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| author | Daniel Borkmann <daniel@iogearbox.net> | 2021-05-21 10:19:22 +0000 |
|---|---|---|
| committer | Daniel Borkmann <daniel@iogearbox.net> | 2021-05-25 22:08:53 +0200 |
| commit | bb01a1bba579b4b1c5566af24d95f1767859771e (patch) | |
| tree | 2a55730fe2493fef3e9067069bed9a5a89bc5ae7 /kernel | |
| parent | 3d0220f6861d713213b015b582e9f21e5b28d2e0 (diff) | |
| download | linux-bb01a1bba579b4b1c5566af24d95f1767859771e.tar.gz linux-bb01a1bba579b4b1c5566af24d95f1767859771e.tar.bz2 linux-bb01a1bba579b4b1c5566af24d95f1767859771e.zip | |
bpf: Fix mask direction swap upon off reg sign change
Masking direction as indicated via mask_to_left is considered to be
calculated once and then used to derive pointer limits. Thus, this
needs to be placed into bpf_sanitize_info instead so we can pass it
to sanitize_ptr_alu() call after the pointer move. Piotr noticed a
corner case where the off reg causes masking direction change which
then results in an incorrect final aux->alu_limit.
Fixes: 7fedb63a8307 ("bpf: Tighten speculative pointer arithmetic mask")
Reported-by: Piotr Krysiuk <piotras@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: Piotr Krysiuk <piotras@gmail.com>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Diffstat (limited to 'kernel')
| -rw-r--r-- | kernel/bpf/verifier.c | 22 |
1 files changed, 12 insertions, 10 deletions
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 98690f5367f9..8574cb60915a 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -6409,18 +6409,10 @@ enum { }; static int retrieve_ptr_limit(const struct bpf_reg_state *ptr_reg, - const struct bpf_reg_state *off_reg, - u32 *alu_limit, u8 opcode) + u32 *alu_limit, bool mask_to_left) { - bool off_is_neg = off_reg->smin_value < 0; - bool mask_to_left = (opcode == BPF_ADD && off_is_neg) || - (opcode == BPF_SUB && !off_is_neg); u32 max = 0, ptr_limit = 0; - if (!tnum_is_const(off_reg->var_off) && - (off_reg->smin_value < 0) != (off_reg->smax_value < 0)) - return REASON_BOUNDS; - switch (ptr_reg->type) { case PTR_TO_STACK: /* Offset 0 is out-of-bounds, but acceptable start for the @@ -6488,6 +6480,7 @@ static bool sanitize_needed(u8 opcode) struct bpf_sanitize_info { struct bpf_insn_aux_data aux; + bool mask_to_left; }; static int sanitize_ptr_alu(struct bpf_verifier_env *env, @@ -6519,7 +6512,16 @@ static int sanitize_ptr_alu(struct bpf_verifier_env *env, if (vstate->speculative) goto do_sim; - err = retrieve_ptr_limit(ptr_reg, off_reg, &alu_limit, opcode); + if (!commit_window) { + if (!tnum_is_const(off_reg->var_off) && + (off_reg->smin_value < 0) != (off_reg->smax_value < 0)) + return REASON_BOUNDS; + + info->mask_to_left = (opcode == BPF_ADD && off_is_neg) || + (opcode == BPF_SUB && !off_is_neg); + } + + err = retrieve_ptr_limit(ptr_reg, &alu_limit, info->mask_to_left); if (err < 0) return err; |