[bpf-next PATCH 02/10] bpf: verifer, refactor adjust_scalar_min_max_vals
From: John Fastabend <john.fastabend@gmail.com>
Date: 2020-03-24 17:38:34
Also in:
bpf
Subsystem:
bpf [core], bpf [general] (safe dynamic programs and tools), the rest · Maintainers:
Alexei Starovoitov, Daniel Borkmann, Andrii Nakryiko, Eduard Zingerman, Kumar Kartikeya Dwivedi, Linus Torvalds
Pull per op ALU logic into individual functions. We are about to add u32 versions of each of these by pull them out the code gets a bit more readable here and nicer in the next patch. Signed-off-by: John Fastabend <john.fastabend@gmail.com> --- kernel/bpf/verifier.c | 403 +++++++++++++++++++++++++++++-------------------- 1 file changed, 239 insertions(+), 164 deletions(-)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 57d3351..f7a34b1 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c@@ -4846,6 +4846,237 @@ static int adjust_ptr_min_max_vals(struct bpf_verifier_env *env, return 0; } +static void scalar_min_max_add(struct bpf_reg_state *dst_reg, + struct bpf_reg_state *src_reg) +{ + s64 smin_val = src_reg->smin_value; + s64 smax_val = src_reg->smax_value; + u64 umin_val = src_reg->umin_value; + u64 umax_val = src_reg->umax_value; + + 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; + dst_reg->smax_value = S64_MAX; + } else { + dst_reg->smin_value += smin_val; + dst_reg->smax_value += smax_val; + } + if (dst_reg->umin_value + umin_val < umin_val || + dst_reg->umax_value + umax_val < umax_val) { + dst_reg->umin_value = 0; + dst_reg->umax_value = U64_MAX; + } else { + dst_reg->umin_value += umin_val; + dst_reg->umax_value += umax_val; + } + dst_reg->var_off = tnum_add(dst_reg->var_off, src_reg->var_off); +} + +static void scalar_min_max_sub(struct bpf_reg_state *dst_reg, + struct bpf_reg_state *src_reg) +{ + s64 smin_val = src_reg->smin_value; + s64 smax_val = src_reg->smax_value; + u64 umin_val = src_reg->umin_value; + u64 umax_val = src_reg->umax_value; + + if (signed_sub_overflows(dst_reg->smin_value, smax_val) || + signed_sub_overflows(dst_reg->smax_value, smin_val)) { + /* Overflow possible, we know nothing */ + dst_reg->smin_value = S64_MIN; + dst_reg->smax_value = S64_MAX; + } else { + dst_reg->smin_value -= smax_val; + dst_reg->smax_value -= smin_val; + } + if (dst_reg->umin_value < umax_val) { + /* Overflow possible, we know nothing */ + dst_reg->umin_value = 0; + dst_reg->umax_value = U64_MAX; + } else { + /* Cannot overflow (as long as bounds are consistent) */ + dst_reg->umin_value -= umax_val; + dst_reg->umax_value -= umin_val; + } + dst_reg->var_off = tnum_sub(dst_reg->var_off, src_reg->var_off); +} + +static void scalar_min_max_mul(struct bpf_reg_state *dst_reg, + struct bpf_reg_state *src_reg) +{ + s64 smin_val = src_reg->smin_value; + u64 umin_val = src_reg->umin_value; + u64 umax_val = src_reg->umax_value; + + dst_reg->var_off = tnum_mul(dst_reg->var_off, src_reg->var_off); + if (smin_val < 0 || dst_reg->smin_value < 0) { + /* Ain't nobody got time to multiply that sign */ + __mark_reg_unbounded(dst_reg); + __update_reg_bounds(dst_reg); + return; + } + /* Both values are positive, so we can work with unsigned and + * copy the result to signed (unless it exceeds S64_MAX). + */ + if (umax_val > U32_MAX || dst_reg->umax_value > U32_MAX) { + /* Potential overflow, we know nothing */ + __mark_reg_unbounded(dst_reg); + /* (except what we can learn from the var_off) */ + __update_reg_bounds(dst_reg); + return; + } + dst_reg->umin_value *= umin_val; + dst_reg->umax_value *= umax_val; + if (dst_reg->umax_value > S64_MAX) { + /* Overflow possible, we know nothing */ + dst_reg->smin_value = S64_MIN; + dst_reg->smax_value = S64_MAX; + } else { + dst_reg->smin_value = dst_reg->umin_value; + dst_reg->smax_value = dst_reg->umax_value; + } +} + +static void scalar_min_max_and(struct bpf_reg_state *dst_reg, + struct bpf_reg_state *src_reg) +{ + s64 smin_val = src_reg->smin_value; + u64 umax_val = src_reg->umax_value; + + /* We get our minimum from the var_off, since that's inherently + * bitwise. Our maximum is the minimum of the operands' maxima. + */ + dst_reg->var_off = tnum_and(dst_reg->var_off, src_reg->var_off); + dst_reg->umin_value = dst_reg->var_off.value; + dst_reg->umax_value = min(dst_reg->umax_value, umax_val); + if (dst_reg->smin_value < 0 || smin_val < 0) { + /* Lose signed bounds when ANDing negative numbers, + * ain't nobody got time for that. + */ + dst_reg->smin_value = S64_MIN; + dst_reg->smax_value = S64_MAX; + } else { + /* ANDing two positives gives a positive, so safe to + * cast result into s64. + */ + dst_reg->smin_value = dst_reg->umin_value; + dst_reg->smax_value = dst_reg->umax_value; + } + /* We may learn something more from the var_off */ + __update_reg_bounds(dst_reg); +} + +static void scalar_min_max_or(struct bpf_reg_state *dst_reg, + struct bpf_reg_state *src_reg) +{ + s64 smin_val = src_reg->smin_value; + u64 umin_val = src_reg->umin_value; + + /* We get our maximum from the var_off, and our minimum is the + * maximum of the operands' minima + */ + dst_reg->var_off = tnum_or(dst_reg->var_off, src_reg->var_off); + dst_reg->umin_value = max(dst_reg->umin_value, umin_val); + dst_reg->umax_value = dst_reg->var_off.value | dst_reg->var_off.mask; + if (dst_reg->smin_value < 0 || smin_val < 0) { + /* Lose signed bounds when ORing negative numbers, + * ain't nobody got time for that. + */ + dst_reg->smin_value = S64_MIN; + dst_reg->smax_value = S64_MAX; + } else { + /* ORing two positives gives a positive, so safe to + * cast result into s64. + */ + dst_reg->smin_value = dst_reg->umin_value; + dst_reg->smax_value = dst_reg->umax_value; + } + /* We may learn something more from the var_off */ + __update_reg_bounds(dst_reg); +} + +static void scalar_min_max_lsh(struct bpf_reg_state *dst_reg, + struct bpf_reg_state *src_reg) +{ + u64 umax_val = src_reg->umax_value; + u64 umin_val = src_reg->umin_value; + + /* We lose all sign bit information (except what we can pick + * up from var_off) + */ + dst_reg->smin_value = S64_MIN; + dst_reg->smax_value = S64_MAX; + /* If we might shift our top bit out, then we know nothing */ + if (dst_reg->umax_value > 1ULL << (63 - umax_val)) { + dst_reg->umin_value = 0; + dst_reg->umax_value = U64_MAX; + } else { + dst_reg->umin_value <<= umin_val; + dst_reg->umax_value <<= umax_val; + } + dst_reg->var_off = tnum_lshift(dst_reg->var_off, umin_val); + /* We may learn something more from the var_off */ + __update_reg_bounds(dst_reg); +} + +static void scalar_min_max_rsh(struct bpf_reg_state *dst_reg, + struct bpf_reg_state *src_reg) +{ + u64 umax_val = src_reg->umax_value; + u64 umin_val = src_reg->umin_value; + + /* BPF_RSH is an unsigned shift. If the value in dst_reg might + * be negative, then either: + * 1) src_reg might be zero, so the sign bit of the result is + * unknown, so we lose our signed bounds + * 2) it's known negative, thus the unsigned bounds capture the + * signed bounds + * 3) the signed bounds cross zero, so they tell us nothing + * about the result + * If the value in dst_reg is known nonnegative, then again the + * unsigned bounts capture the signed bounds. + * Thus, in all cases it suffices to blow away our signed bounds + * and rely on inferring new ones from the unsigned bounds and + * var_off of the result. + */ + dst_reg->smin_value = S64_MIN; + dst_reg->smax_value = S64_MAX; + dst_reg->var_off = tnum_rshift(dst_reg->var_off, umin_val); + dst_reg->umin_value >>= umax_val; + dst_reg->umax_value >>= umin_val; + /* We may learn something more from the var_off */ + __update_reg_bounds(dst_reg); +} + +static void scalar_min_max_arsh(struct bpf_reg_state *dst_reg, + struct bpf_reg_state *src_reg, + u64 insn_bitness) +{ + u64 umin_val = src_reg->umin_value; + + /* Upon reaching here, src_known is true and + * umax_val is equal to umin_val. + */ + if (insn_bitness == 32) { + dst_reg->smin_value = (u32)(((s32)dst_reg->smin_value) >> umin_val); + dst_reg->smax_value = (u32)(((s32)dst_reg->smax_value) >> umin_val); + } else { + dst_reg->smin_value >>= umin_val; + dst_reg->smax_value >>= umin_val; + } + + dst_reg->var_off = tnum_arshift(dst_reg->var_off, umin_val, + insn_bitness); + + /* blow away the dst_reg umin_value/umax_value and rely on + * dst_reg var_off to refine the result. + */ + dst_reg->umin_value = 0; + dst_reg->umax_value = U64_MAX; + __update_reg_bounds(dst_reg); +} + /* WARNING: This function does calculations on 64-bit values, but the actual * execution may occur on 32-bit values. Therefore, things like bitshifts * need extra checks in the 32-bit case.
@@ -4902,23 +5133,7 @@ static int adjust_scalar_min_max_vals(struct bpf_verifier_env *env, 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; - dst_reg->smax_value = S64_MAX; - } else { - dst_reg->smin_value += smin_val; - dst_reg->smax_value += smax_val; - } - if (dst_reg->umin_value + umin_val < umin_val || - dst_reg->umax_value + umax_val < umax_val) { - dst_reg->umin_value = 0; - dst_reg->umax_value = U64_MAX; - } else { - dst_reg->umin_value += umin_val; - dst_reg->umax_value += umax_val; - } - dst_reg->var_off = tnum_add(dst_reg->var_off, src_reg.var_off); + scalar_min_max_add(dst_reg, &src_reg); break; case BPF_SUB: ret = sanitize_val_alu(env, insn);
@@ -4926,54 +5141,10 @@ static int adjust_scalar_min_max_vals(struct bpf_verifier_env *env, 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 */ - dst_reg->smin_value = S64_MIN; - dst_reg->smax_value = S64_MAX; - } else { - dst_reg->smin_value -= smax_val; - dst_reg->smax_value -= smin_val; - } - if (dst_reg->umin_value < umax_val) { - /* Overflow possible, we know nothing */ - dst_reg->umin_value = 0; - dst_reg->umax_value = U64_MAX; - } else { - /* Cannot overflow (as long as bounds are consistent) */ - dst_reg->umin_value -= umax_val; - dst_reg->umax_value -= umin_val; - } - dst_reg->var_off = tnum_sub(dst_reg->var_off, src_reg.var_off); + scalar_min_max_sub(dst_reg, &src_reg); break; case BPF_MUL: - dst_reg->var_off = tnum_mul(dst_reg->var_off, src_reg.var_off); - if (smin_val < 0 || dst_reg->smin_value < 0) { - /* Ain't nobody got time to multiply that sign */ - __mark_reg_unbounded(dst_reg); - __update_reg_bounds(dst_reg); - break; - } - /* Both values are positive, so we can work with unsigned and - * copy the result to signed (unless it exceeds S64_MAX). - */ - if (umax_val > U32_MAX || dst_reg->umax_value > U32_MAX) { - /* Potential overflow, we know nothing */ - __mark_reg_unbounded(dst_reg); - /* (except what we can learn from the var_off) */ - __update_reg_bounds(dst_reg); - break; - } - dst_reg->umin_value *= umin_val; - dst_reg->umax_value *= umax_val; - if (dst_reg->umax_value > S64_MAX) { - /* Overflow possible, we know nothing */ - dst_reg->smin_value = S64_MIN; - dst_reg->smax_value = S64_MAX; - } else { - dst_reg->smin_value = dst_reg->umin_value; - dst_reg->smax_value = dst_reg->umax_value; - } + scalar_min_max_mul(dst_reg, &src_reg); break; case BPF_AND: if (src_known && dst_known) {
@@ -4981,27 +5152,7 @@ static int adjust_scalar_min_max_vals(struct bpf_verifier_env *env, src_reg.var_off.value); break; } - /* We get our minimum from the var_off, since that's inherently - * bitwise. Our maximum is the minimum of the operands' maxima. - */ - dst_reg->var_off = tnum_and(dst_reg->var_off, src_reg.var_off); - dst_reg->umin_value = dst_reg->var_off.value; - dst_reg->umax_value = min(dst_reg->umax_value, umax_val); - if (dst_reg->smin_value < 0 || smin_val < 0) { - /* Lose signed bounds when ANDing negative numbers, - * ain't nobody got time for that. - */ - dst_reg->smin_value = S64_MIN; - dst_reg->smax_value = S64_MAX; - } else { - /* ANDing two positives gives a positive, so safe to - * cast result into s64. - */ - dst_reg->smin_value = dst_reg->umin_value; - dst_reg->smax_value = dst_reg->umax_value; - } - /* We may learn something more from the var_off */ - __update_reg_bounds(dst_reg); + scalar_min_max_and(dst_reg, &src_reg); break; case BPF_OR: if (src_known && dst_known) {
@@ -5009,28 +5160,7 @@ static int adjust_scalar_min_max_vals(struct bpf_verifier_env *env, src_reg.var_off.value); break; } - /* We get our maximum from the var_off, and our minimum is the - * maximum of the operands' minima - */ - dst_reg->var_off = tnum_or(dst_reg->var_off, src_reg.var_off); - dst_reg->umin_value = max(dst_reg->umin_value, umin_val); - dst_reg->umax_value = dst_reg->var_off.value | - dst_reg->var_off.mask; - if (dst_reg->smin_value < 0 || smin_val < 0) { - /* Lose signed bounds when ORing negative numbers, - * ain't nobody got time for that. - */ - dst_reg->smin_value = S64_MIN; - dst_reg->smax_value = S64_MAX; - } else { - /* ORing two positives gives a positive, so safe to - * cast result into s64. - */ - dst_reg->smin_value = dst_reg->umin_value; - dst_reg->smax_value = dst_reg->umax_value; - } - /* We may learn something more from the var_off */ - __update_reg_bounds(dst_reg); + scalar_min_max_or(dst_reg, &src_reg); break; case BPF_LSH: if (umax_val >= insn_bitness) {
@@ -5040,22 +5170,7 @@ static int adjust_scalar_min_max_vals(struct bpf_verifier_env *env, mark_reg_unknown(env, regs, insn->dst_reg); break; } - /* We lose all sign bit information (except what we can pick - * up from var_off) - */ - dst_reg->smin_value = S64_MIN; - dst_reg->smax_value = S64_MAX; - /* If we might shift our top bit out, then we know nothing */ - if (dst_reg->umax_value > 1ULL << (63 - umax_val)) { - dst_reg->umin_value = 0; - dst_reg->umax_value = U64_MAX; - } else { - dst_reg->umin_value <<= umin_val; - dst_reg->umax_value <<= umax_val; - } - dst_reg->var_off = tnum_lshift(dst_reg->var_off, umin_val); - /* We may learn something more from the var_off */ - __update_reg_bounds(dst_reg); + scalar_min_max_lsh(dst_reg, &src_reg); break; case BPF_RSH: if (umax_val >= insn_bitness) {
@@ -5065,27 +5180,7 @@ static int adjust_scalar_min_max_vals(struct bpf_verifier_env *env, mark_reg_unknown(env, regs, insn->dst_reg); break; } - /* BPF_RSH is an unsigned shift. If the value in dst_reg might - * be negative, then either: - * 1) src_reg might be zero, so the sign bit of the result is - * unknown, so we lose our signed bounds - * 2) it's known negative, thus the unsigned bounds capture the - * signed bounds - * 3) the signed bounds cross zero, so they tell us nothing - * about the result - * If the value in dst_reg is known nonnegative, then again the - * unsigned bounts capture the signed bounds. - * Thus, in all cases it suffices to blow away our signed bounds - * and rely on inferring new ones from the unsigned bounds and - * var_off of the result. - */ - dst_reg->smin_value = S64_MIN; - dst_reg->smax_value = S64_MAX; - dst_reg->var_off = tnum_rshift(dst_reg->var_off, umin_val); - dst_reg->umin_value >>= umax_val; - dst_reg->umax_value >>= umin_val; - /* We may learn something more from the var_off */ - __update_reg_bounds(dst_reg); + scalar_min_max_rsh(dst_reg, &src_reg); break; case BPF_ARSH: if (umax_val >= insn_bitness) {
@@ -5095,27 +5190,7 @@ static int adjust_scalar_min_max_vals(struct bpf_verifier_env *env, mark_reg_unknown(env, regs, insn->dst_reg); break; } - - /* Upon reaching here, src_known is true and - * umax_val is equal to umin_val. - */ - if (insn_bitness == 32) { - dst_reg->smin_value = (u32)(((s32)dst_reg->smin_value) >> umin_val); - dst_reg->smax_value = (u32)(((s32)dst_reg->smax_value) >> umin_val); - } else { - dst_reg->smin_value >>= umin_val; - dst_reg->smax_value >>= umin_val; - } - - dst_reg->var_off = tnum_arshift(dst_reg->var_off, umin_val, - insn_bitness); - - /* blow away the dst_reg umin_value/umax_value and rely on - * dst_reg var_off to refine the result. - */ - dst_reg->umin_value = 0; - dst_reg->umax_value = U64_MAX; - __update_reg_bounds(dst_reg); + scalar_min_max_arsh(dst_reg, &src_reg, insn_bitness); break; default: mark_reg_unknown(env, regs, insn->dst_reg);