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bpf: smarter verifier log number printing logic
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Instead of always printing numbers as either decimals (and in some
cases, like for "imm=%llx", in hexadecimals), decide the form based on
actual values. For numbers in a reasonably small range (currently,
[0, U16_MAX] for unsigned values, and [S16_MIN, S16_MAX] for signed ones),
emit them as decimals. In all other cases, even for signed values,
emit them in hexadecimals.

For large values hex form is often times way more useful: it's easier to
see an exact difference between 0xffffffff80000000 and 0xffffffff7fffffff,
than between 18446744071562067966 and 18446744071562067967, as one
particular example.

Small values representing small pointer offsets or application
constants, on the other hand, are way more useful to be represented in
decimal notation.

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
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@anakryiko @d-e-s-o
anakryiko authored and d-e-s-o committed Nov 10, 2023
1 parent ec70c98 commit 490635b
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Showing 2 changed files with 76 additions and 23 deletions.
67 changes: 60 additions & 7 deletions kernel/bpf/log.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -509,10 +509,52 @@ static void print_liveness(struct bpf_verifier_env *env,
verbose(env, "D");
}

#define UNUM_MAX_DECIMAL U16_MAX
#define SNUM_MAX_DECIMAL S16_MAX
#define SNUM_MIN_DECIMAL S16_MIN

static bool is_unum_decimal(u64 num)
{
return num <= UNUM_MAX_DECIMAL;
}

static bool is_snum_decimal(s64 num)
{
return num >= SNUM_MIN_DECIMAL && num <= SNUM_MAX_DECIMAL;
}

static void verbose_unum(struct bpf_verifier_env *env, u64 num)
{
if (is_unum_decimal(num))
verbose(env, "%llu", num);
else
verbose(env, "%#llx", num);
}

static void verbose_snum(struct bpf_verifier_env *env, s64 num)
{
if (is_snum_decimal(num))
verbose(env, "%lld", num);
else
verbose(env, "%#llx", num);
}

static void print_scalar_ranges(struct bpf_verifier_env *env,
const struct bpf_reg_state *reg,
const char **sep)
{
/* For signed ranges, we want to unify 64-bit and 32-bit values in the
* output as much as possible, but there is a bit of a complication.
* If we choose to print values as decimals, this is natural to do,
* because negative 64-bit and 32-bit values >= -S32_MIN have the same
* representation due to sign extension. But if we choose to print
* them in hex format (see is_snum_decimal()), then sign extension is
* misleading.
* E.g., smin=-2 and smin32=-2 are exactly the same in decimal, but in
* hex they will be smin=0xfffffffffffffffe and smin32=0xfffffffe, two
* very different numbers.
* So we avoid sign extension if we choose to print values in hex.
*/
struct {
const char *name;
u64 val;
Expand All @@ -522,8 +564,14 @@ static void print_scalar_ranges(struct bpf_verifier_env *env,
{"smax", reg->smax_value, reg->smax_value == S64_MAX},
{"umin", reg->umin_value, reg->umin_value == 0},
{"umax", reg->umax_value, reg->umax_value == U64_MAX},
{"smin32", (s64)reg->s32_min_value, reg->s32_min_value == S32_MIN},
{"smax32", (s64)reg->s32_max_value, reg->s32_max_value == S32_MAX},
{"smin32",
is_snum_decimal((s64)reg->s32_min_value)
? (s64)reg->s32_min_value
: (u32)reg->s32_min_value, reg->s32_min_value == S32_MIN},
{"smax32",
is_snum_decimal((s64)reg->s32_max_value)
? (s64)reg->s32_max_value
: (u32)reg->s32_max_value, reg->s32_max_value == S32_MAX},
{"umin32", reg->u32_min_value, reg->u32_min_value == 0},
{"umax32", reg->u32_max_value, reg->u32_max_value == U32_MAX},
}, *m1, *m2, *mend = &minmaxs[ARRAY_SIZE(minmaxs)];
Expand All @@ -549,7 +597,10 @@ static void print_scalar_ranges(struct bpf_verifier_env *env,
verbose(env, "%s=", m2->name);
}

verbose(env, m1->name[0] == 's' ? "%lld" : "%llu", m1->val);
if (m1->name[0] == 's')
verbose_snum(env, m1->val);
else
verbose_unum(env, m1->val);
}
}

Expand All @@ -576,14 +627,14 @@ static void print_reg_state(struct bpf_verifier_env *env, const struct bpf_reg_s
tnum_is_const(reg->var_off)) {
/* reg->off should be 0 for SCALAR_VALUE */
verbose(env, "%s", t == SCALAR_VALUE ? "" : reg_type_str(env, t));
verbose(env, "%lld", reg->var_off.value + reg->off);
verbose_snum(env, reg->var_off.value + reg->off);
return;
}
/*
* _a stands for append, was shortened to avoid multiline statements below.
* This macro is used to output a comma separated list of attributes.
*/
#define verbose_a(fmt, ...) ({ verbose(env, "%s" fmt, sep, __VA_ARGS__); sep = ","; })
#define verbose_a(fmt, ...) ({ verbose(env, "%s" fmt, sep, ##__VA_ARGS__); sep = ","; })

verbose(env, "%s", reg_type_str(env, t));
if (base_type(t) == PTR_TO_BTF_ID)
Expand All @@ -608,8 +659,10 @@ static void print_reg_state(struct bpf_verifier_env *env, const struct bpf_reg_s
verbose_a("r=%d", reg->range);
if (tnum_is_const(reg->var_off)) {
/* a pointer register with fixed offset */
if (reg->var_off.value)
verbose_a("imm=%llx", reg->var_off.value);
if (reg->var_off.value) {
verbose_a("imm=");
verbose_snum(env, reg->var_off.value);
}
} else {
print_scalar_ranges(env, reg, &sep);
if (!tnum_is_unknown(reg->var_off)) {
Expand Down
32 changes: 16 additions & 16 deletions tools/testing/selftests/bpf/progs/exceptions_assert.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -18,48 +18,48 @@
return *(u64 *)num; \
}

__msg(": R0_w=-2147483648 R10=fp0")
__msg(": R0_w=0xffffffff80000000 R10=fp0")
check_assert(s64, eq, int_min, INT_MIN);
__msg(": R0_w=2147483647 R10=fp0")
__msg(": R0_w=0x7fffffff R10=fp0")
check_assert(s64, eq, int_max, INT_MAX);
__msg(": R0_w=0 R10=fp0")
check_assert(s64, eq, zero, 0);
__msg(": R0_w=-9223372036854775808 R1_w=-9223372036854775808 R10=fp0")
__msg(": R0_w=0x8000000000000000 R1_w=0x8000000000000000 R10=fp0")
check_assert(s64, eq, llong_min, LLONG_MIN);
__msg(": R0_w=9223372036854775807 R1_w=9223372036854775807 R10=fp0")
__msg(": R0_w=0x7fffffffffffffff R1_w=0x7fffffffffffffff R10=fp0")
check_assert(s64, eq, llong_max, LLONG_MAX);

__msg(": R0_w=scalar(smax=2147483646) R10=fp0")
__msg(": R0_w=scalar(smax=0x7ffffffe) R10=fp0")
check_assert(s64, lt, pos, INT_MAX);
__msg(": R0_w=scalar(smax=-1,umin=9223372036854775808,var_off=(0x8000000000000000; 0x7fffffffffffffff))")
__msg(": R0_w=scalar(smax=-1,umin=0x8000000000000000,var_off=(0x8000000000000000; 0x7fffffffffffffff))")
check_assert(s64, lt, zero, 0);
__msg(": R0_w=scalar(smax=-2147483649,umin=9223372036854775808,umax=18446744071562067967,var_off=(0x8000000000000000; 0x7fffffffffffffff))")
__msg(": R0_w=scalar(smax=0xffffffff7fffffff,umin=0x8000000000000000,umax=0xffffffff7fffffff,var_off=(0x8000000000000000; 0x7fffffffffffffff))")
check_assert(s64, lt, neg, INT_MIN);

__msg(": R0_w=scalar(smax=2147483647) R10=fp0")
__msg(": R0_w=scalar(smax=0x7fffffff) R10=fp0")
check_assert(s64, le, pos, INT_MAX);
__msg(": R0_w=scalar(smax=0) R10=fp0")
check_assert(s64, le, zero, 0);
__msg(": R0_w=scalar(smax=-2147483648,umin=9223372036854775808,umax=18446744071562067968,var_off=(0x8000000000000000; 0x7fffffffffffffff))")
__msg(": R0_w=scalar(smax=0xffffffff80000000,umin=0x8000000000000000,umax=0xffffffff80000000,var_off=(0x8000000000000000; 0x7fffffffffffffff))")
check_assert(s64, le, neg, INT_MIN);

__msg(": R0_w=scalar(smin=umin=2147483648,umax=9223372036854775807,var_off=(0x0; 0x7fffffffffffffff))")
__msg(": R0_w=scalar(smin=umin=0x80000000,umax=0x7fffffffffffffff,var_off=(0x0; 0x7fffffffffffffff))")
check_assert(s64, gt, pos, INT_MAX);
__msg(": R0_w=scalar(smin=umin=1,umax=9223372036854775807,var_off=(0x0; 0x7fffffffffffffff))")
__msg(": R0_w=scalar(smin=umin=1,umax=0x7fffffffffffffff,var_off=(0x0; 0x7fffffffffffffff))")
check_assert(s64, gt, zero, 0);
__msg(": R0_w=scalar(smin=-2147483647) R10=fp0")
__msg(": R0_w=scalar(smin=0xffffffff80000001) R10=fp0")
check_assert(s64, gt, neg, INT_MIN);

__msg(": R0_w=scalar(smin=umin=2147483647,umax=9223372036854775807,var_off=(0x0; 0x7fffffffffffffff))")
__msg(": R0_w=scalar(smin=umin=0x7fffffff,umax=0x7fffffffffffffff,var_off=(0x0; 0x7fffffffffffffff))")
check_assert(s64, ge, pos, INT_MAX);
__msg(": R0_w=scalar(smin=0,umax=9223372036854775807,var_off=(0x0; 0x7fffffffffffffff)) R10=fp0")
__msg(": R0_w=scalar(smin=0,umax=0x7fffffffffffffff,var_off=(0x0; 0x7fffffffffffffff)) R10=fp0")
check_assert(s64, ge, zero, 0);
__msg(": R0_w=scalar(smin=-2147483648) R10=fp0")
__msg(": R0_w=scalar(smin=0xffffffff80000000) R10=fp0")
check_assert(s64, ge, neg, INT_MIN);

SEC("?tc")
__log_level(2) __failure
__msg(": R0=0 R1=ctx() R2=scalar(smin=smin32=-2147483646,smax=smax32=2147483645) R10=fp0")
__msg(": R0=0 R1=ctx() R2=scalar(smin=0xffffffff80000002,smax=smax32=0x7ffffffd,smin32=0x80000002) R10=fp0")
int check_assert_range_s64(struct __sk_buff *ctx)
{
struct bpf_sock *sk = ctx->sk;
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