Same as in __reg64_deduce_bounds(), refine s32/u32 ranges in __reg32_deduce_bounds() in the following situations: 0 U32_MAX | [xxxxxxxxxxxxxx u32 range xxxxxxxxxxxxxx] | |----------------------------|----------------------------| |xxxxx s32 range xxxxxxxxx] [xxxxxxx| 0 S32_MAX S32_MIN -1 0 U32_MAX | [xxxxxxxxxxxxxx u32 range xxxxxxxxxxxxxx] | |----------------------------|----------------------------| |xxxxxxxxx] [xxxxxxxxxxxx s32 range | 0 S32_MAX S32_MIN -1 This helps for e.g. consider the following program: call %[bpf_get_prandom_u32]; w0 &= 0xffffffff; if w0 < 0x3 goto 1f; // on fall-through u32 range [3..U32_MAX] if w0 s> 0x1 goto 1f; // on fall-through s32 range [S32_MIN..1] if w0 s< 0x0 goto 1f; // range can be narrowed to [S32_MIN..-1] r10 = 0; 1: ...; The reg_bounds.c selftest is updated to incorporate identical logic, refinement based on non-overflowing range halves: ((x ∩ [0, smax]) ∩ (y ∩ [0, smax])) ∪ ((x ∩ [smin,-1]) ∩ (y ∩ [smin,-1])) Reported-by: Andrea Righi Reported-by: Emil Tsalapatis Closes: https://lore.kernel.org/bpf/aakqucg4vcujVwif@gpd4/T/ Signed-off-by: Eduard Zingerman --- kernel/bpf/verifier.c | 24 ++++++++ .../selftests/bpf/prog_tests/reg_bounds.c | 58 +++++++++++++++++-- 2 files changed, 78 insertions(+), 4 deletions(-) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index d92cf2821657..2b79a2a4d1b5 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -2532,6 +2532,30 @@ static void __reg32_deduce_bounds(struct bpf_reg_state *reg) if ((u32)reg->s32_min_value <= (u32)reg->s32_max_value) { reg->u32_min_value = max_t(u32, reg->s32_min_value, reg->u32_min_value); reg->u32_max_value = min_t(u32, reg->s32_max_value, reg->u32_max_value); + } else { + if (reg->u32_max_value < (u32)reg->s32_min_value) { + /* See __reg64_deduce_bounds() for detailed explanation. + * Refine ranges in the following situation: + * + * 0 U32_MAX + * | [xxxxxxxxxxxxxx u32 range xxxxxxxxxxxxxx] | + * |----------------------------|----------------------------| + * |xxxxx s32 range xxxxxxxxx] [xxxxxxx| + * 0 S32_MAX S32_MIN -1 + */ + reg->s32_min_value = (s32)reg->u32_min_value; + reg->u32_max_value = min_t(u32, reg->u32_max_value, reg->s32_max_value); + } else if ((u32)reg->s32_max_value < reg->u32_min_value) { + /* + * 0 U32_MAX + * | [xxxxxxxxxxxxxx u32 range xxxxxxxxxxxxxx] | + * |----------------------------|----------------------------| + * |xxxxxxxxx] [xxxxxxxxxxxx s32 range | + * 0 S32_MAX S32_MIN -1 + */ + reg->s32_max_value = (s32)reg->u32_max_value; + reg->u32_min_value = max_t(u32, reg->u32_min_value, reg->s32_min_value); + } } } diff --git a/tools/testing/selftests/bpf/prog_tests/reg_bounds.c b/tools/testing/selftests/bpf/prog_tests/reg_bounds.c index 0322f817d07b..446e5ef62f44 100644 --- a/tools/testing/selftests/bpf/prog_tests/reg_bounds.c +++ b/tools/testing/selftests/bpf/prog_tests/reg_bounds.c @@ -422,15 +422,65 @@ static bool is_valid_range(enum num_t t, struct range x) } } -static struct range range_improve(enum num_t t, struct range old, struct range new) +static struct range range_intersection(enum num_t t, struct range old, struct range new) { return range(t, max_t(t, old.a, new.a), min_t(t, old.b, new.b)); } +static struct range range_union(enum num_t t, struct range x, struct range y) +{ + if (!is_valid_range(t, x)) + return y; + if (!is_valid_range(t, y)) + return x; + return range(t, min_t(t, x.a, y.a), max_t(t, x.b, y.b)); +} + +/* + * This function attempts to improve x range intersecting it with y. + * range_cast(... to_t ...) looses precision for ranges that pass to_t + * min/max boundaries. To avoid such precision loses this function + * splits both x and y into halves corresponding to non-overflowing + * sub-ranges: [0, smin] and [smax, -1]. + * Final result is computed as follows: + * + * ((x ∩ [0, smax]) ∩ (y ∩ [0, smax])) ∪ + * ((x ∩ [smin,-1]) ∩ (y ∩ [smin,-1])) + * + * Precision might still be lost if final union is not a continuous range. + */ +static struct range range_refine_in_halves(enum num_t x_t, struct range x, + enum num_t y_t, struct range y) +{ + struct range x_pos, x_neg, y_pos, y_neg, r_pos, r_neg; + u64 smax, smin, neg_one; + + if (t_is_32(x_t)) { + smax = (u64)(u32)S32_MAX; + smin = (u64)(u32)S32_MIN; + neg_one = (u64)(u32)(s32)(-1); + } else { + smax = (u64)S64_MAX; + smin = (u64)S64_MIN; + neg_one = U64_MAX; + } + x_pos = range_intersection(x_t, x, range(x_t, 0, smax)); + x_neg = range_intersection(x_t, x, range(x_t, smin, neg_one)); + y_pos = range_intersection(y_t, y, range(x_t, 0, smax)); + y_neg = range_intersection(y_t, y, range(y_t, smin, neg_one)); + r_pos = range_intersection(x_t, x_pos, range_cast(y_t, x_t, y_pos)); + r_neg = range_intersection(x_t, x_neg, range_cast(y_t, x_t, y_neg)); + return range_union(x_t, r_pos, r_neg); + +} + static struct range range_refine(enum num_t x_t, struct range x, enum num_t y_t, struct range y) { struct range y_cast; + if (t_is_32(x_t) == t_is_32(y_t)) + x = range_refine_in_halves(x_t, x, y_t, y); + y_cast = range_cast(y_t, x_t, y); /* If we know that @@ -444,7 +494,7 @@ static struct range range_refine(enum num_t x_t, struct range x, enum num_t y_t, */ if (x_t == S64 && y_t == S32 && y_cast.a <= S32_MAX && y_cast.b <= S32_MAX && (s64)x.a >= S32_MIN && (s64)x.b <= S32_MAX) - return range_improve(x_t, x, y_cast); + return range_intersection(x_t, x, y_cast); /* the case when new range knowledge, *y*, is a 32-bit subregister * range, while previous range knowledge, *x*, is a full register @@ -462,7 +512,7 @@ static struct range range_refine(enum num_t x_t, struct range x, enum num_t y_t, x_swap = range(x_t, swap_low32(x.a, y_cast.a), swap_low32(x.b, y_cast.b)); if (!is_valid_range(x_t, x_swap)) return x; - return range_improve(x_t, x, x_swap); + return range_intersection(x_t, x, x_swap); } if (!t_is_32(x_t) && !t_is_32(y_t) && x_t != y_t) { @@ -480,7 +530,7 @@ static struct range range_refine(enum num_t x_t, struct range x, enum num_t y_t, } /* otherwise, plain range cast and intersection works */ - return range_improve(x_t, x, y_cast); + return range_intersection(x_t, x, y_cast); } /* ======================= -- 2.51.1 Two test cases for signed/unsigned 32-bit bounds refinement when s32 range crosses the sign boundary: - s32 range [S32_MIN..1] overlapping with u32 range [3..U32_MAX], s32 range tail before sign boundary overlaps with u32 range. - s32 range [-3..5] overlapping with u32 range [0..S32_MIN+3], s32 range head after the sign boundary overlaps with u32 range. This covers both branches added in the __reg32_deduce_bounds(). Signed-off-by: Eduard Zingerman --- .../selftests/bpf/progs/verifier_bounds.c | 37 +++++++++++++++++++ 1 file changed, 37 insertions(+) diff --git a/tools/testing/selftests/bpf/progs/verifier_bounds.c b/tools/testing/selftests/bpf/progs/verifier_bounds.c index 4588e5b55b41..0c2a62b16ec4 100644 --- a/tools/testing/selftests/bpf/progs/verifier_bounds.c +++ b/tools/testing/selftests/bpf/progs/verifier_bounds.c @@ -2000,4 +2000,41 @@ __naked void bounds_refinement_multiple_overlaps(void *ctx) : __clobber_all); } +SEC("socket") +__success +__flag(BPF_F_TEST_REG_INVARIANTS) +__naked void signed_unsigned_intersection32_case1(void *ctx) +{ + asm volatile(" \ + call %[bpf_get_prandom_u32]; \ + w0 &= 0xffffffff; \ + if w0 < 0x3 goto 1f; /* on fall-through u32 range [3..U32_MAX] */ \ + if w0 s> 0x1 goto 1f; /* on fall-through s32 range [S32_MIN..1] */ \ + if w0 s< 0x0 goto 1f; /* range can be narrowed to [S32_MIN..-1] */ \ + r10 = 0; /* thus predicting the jump. */ \ +1: exit; \ +" : + : __imm(bpf_get_prandom_u32) + : __clobber_all); +} + +SEC("socket") +__success +__flag(BPF_F_TEST_REG_INVARIANTS) +__naked void signed_unsigned_intersection32_case2(void *ctx) +{ + asm volatile(" \ + call %[bpf_get_prandom_u32]; \ + w0 &= 0xffffffff; \ + if w0 > 0x80000003 goto 1f; /* on fall-through u32 range [0..S32_MIN+3] */ \ + if w0 s< -3 goto 1f; /* on fall-through s32 range [-3..S32_MAX] */ \ + if w0 s> 5 goto 1f; /* on fall-through s32 range [-3..5] */ \ + if w0 <= 5 goto 1f; /* range can be narrowed to [0..5] */ \ + r10 = 0; /* thus predicting the jump */ \ +1: exit; \ +" : + : __imm(bpf_get_prandom_u32) + : __clobber_all); +} + char _license[] SEC("license") = "GPL"; -- 2.51.1