Re: [PATCH v5 bpf-next 15/23] bpf: unify 32-bit and 64-bit is_branch_taken logic

Eduard Zingerman
2023-10-31T17:36:01Z

On Fri, 2023-10-27 at 11:13 -0700, Andrii Nakryiko wrote:
> Combine 32-bit and 64-bit is_branch_taken logic for SCALAR_VALUE
> registers. It makes it easier to see parallels between two domains
> (32-bit and 64-bit), and makes subsequent refactoring more
> straightforward.
>
> No functional changes.
>
> Signed-off-by: Andrii Nakryiko <andrii@kernel.org>

Acked-by: Eduard Zingerman <eddyz87@gmail.com>

> ---
> kernel/bpf/verifier.c | 154 ++++++++++--------------------------------
> 1 file changed, 36 insertions(+), 118 deletions(-)
>
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index fedd6d0e76e5..b911d1111fad 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -14185,166 +14185,86 @@ static u64 reg_const_value(struct bpf_reg_state *reg, bool subreg32)
> /*
> * <reg1> <op> <reg2>, currently assuming reg2 is a constant
> */
> -static int is_branch32_taken(struct bpf_reg_state *reg1, struct bpf_reg_state *reg2, u8 opcode)
> +static int is_scalar_branch_taken(struct bpf_reg_state *reg1, struct bpf_reg_state *reg2,
> + u8 opcode, bool is_jmp32)
> {
> - struct tnum subreg = tnum_subreg(reg1->var_off);
> - u32 val = (u32)tnum_subreg(reg2->var_off).value;
> - s32 sval = (s32)val;
> + struct tnum t1 = is_jmp32 ? tnum_subreg(reg1->var_off) : reg1->var_off;
> + u64 umin1 = is_jmp32 ? (u64)reg1->u32_min_value : reg1->umin_value;
> + u64 umax1 = is_jmp32 ? (u64)reg1->u32_max_value : reg1->umax_value;
> + s64 smin1 = is_jmp32 ? (s64)reg1->s32_min_value : reg1->smin_value;
> + s64 smax1 = is_jmp32 ? (s64)reg1->s32_max_value : reg1->smax_value;
> + u64 val = is_jmp32 ? (u32)tnum_subreg(reg2->var_off).value : reg2->var_off.value;
> + s64 sval = is_jmp32 ? (s32)val : (s64)val;
>
> switch (opcode) {
> case BPF_JEQ:
> - if (tnum_is_const(subreg))
> - return !!tnum_equals_const(subreg, val);
> - else if (val < reg1->u32_min_value || val > reg1->u32_max_value)
> + if (tnum_is_const(t1))
> + return !!tnum_equals_const(t1, val);
> + else if (val < umin1 || val > umax1)
> return 0;
> - else if (sval < reg1->s32_min_value || sval > reg1->s32_max_value)
> + else if (sval < smin1 || sval > smax1)
> return 0;
> break;
> case BPF_JNE:
> - if (tnum_is_const(subreg))
> - return !tnum_equals_const(subreg, val);
> - else if (val < reg1->u32_min_value || val > reg1->u32_max_value)
> + if (tnum_is_const(t1))
> + return !tnum_equals_const(t1, val);
> + else if (val < umin1 || val > umax1)
> return 1;
> - else if (sval < reg1->s32_min_value || sval > reg1->s32_max_value)
> + else if (sval < smin1 || sval > smax1)
> return 1;
> break;
> case BPF_JSET:
> - if ((~subreg.mask & subreg.value) & val)
> + if ((~t1.mask & t1.value) & val)
> return 1;
> - if (!((subreg.mask | subreg.value) & val))
> + if (!((t1.mask | t1.value) & val))
> return 0;
> break;
> case BPF_JGT:
> - if (reg1->u32_min_value > val)
> + if (umin1 > val )
> return 1;
> - else if (reg1->u32_max_value <= val)
> + else if (umax1 <= val)
> return 0;
> break;
> case BPF_JSGT:
> - if (reg1->s32_min_value > sval)
> + if (smin1 > sval)
> return 1;
> - else if (reg1->s32_max_value <= sval)
> + else if (smax1 <= sval)
> return 0;
> break;
> case BPF_JLT:
> - if (reg1->u32_max_value < val)
> + if (umax1 < val)
> return 1;
> - else if (reg1->u32_min_value >= val)
> + else if (umin1 >= val)
> return 0;
> break;
> case BPF_JSLT:
> - if (reg1->s32_max_value < sval)
> + if (smax1 < sval)
> return 1;
> - else if (reg1->s32_min_value >= sval)
> + else if (smin1 >= sval)
> return 0;
> break;
> case BPF_JGE:
> - if (reg1->u32_min_value >= val)
> + if (umin1 >= val)
> return 1;
> - else if (reg1->u32_max_value < val)
> + else if (umax1 < val)
> return 0;
> break;
> case BPF_JSGE:
> - if (reg1->s32_min_value >= sval)
> + if (smin1 >= sval)
> return 1;
> - else if (reg1->s32_max_value < sval)
> + else if (smax1 < sval)
> return 0;
> break;
> case BPF_JLE:
> - if (reg1->u32_max_value <= val)
> + if (umax1 <= val)
> return 1;
> - else if (reg1->u32_min_value > val)
> + else if (umin1 > val)
> return 0;
> break;
> case BPF_JSLE:
> - if (reg1->s32_max_value <= sval)
> + if (smax1 <= sval)
> return 1;
> - else if (reg1->s32_min_value > sval)
> - return 0;
> - break;
> - }
> -
> - return -1;
> -}
> -
> -
> -/*
> - * <reg1> <op> <reg2>, currently assuming reg2 is a constant
> - */
> -static int is_branch64_taken(struct bpf_reg_state *reg1, struct bpf_reg_state *reg2, u8 opcode)
> -{
> - u64 val = reg2->var_off.value;
> - s64 sval = (s64)val;
> -
> - switch (opcode) {
> - case BPF_JEQ:
> - if (tnum_is_const(reg1->var_off))
> - return !!tnum_equals_const(reg1->var_off, val);
> - else if (val < reg1->umin_value || val > reg1->umax_value)
> - return 0;
> - else if (sval < reg1->smin_value || sval > reg1->smax_value)
> - return 0;
> - break;
> - case BPF_JNE:
> - if (tnum_is_const(reg1->var_off))
> - return !tnum_equals_const(reg1->var_off, val);
> - else if (val < reg1->umin_value || val > reg1->umax_value)
> - return 1;
> - else if (sval < reg1->smin_value || sval > reg1->smax_value)
> - return 1;
> - break;
> - case BPF_JSET:
> - if ((~reg1->var_off.mask & reg1->var_off.value) & val)
> - return 1;
> - if (!((reg1->var_off.mask | reg1->var_off.value) & val))
> - return 0;
> - break;
> - case BPF_JGT:
> - if (reg1->umin_value > val)
> - return 1;
> - else if (reg1->umax_value <= val)
> - return 0;
> - break;
> - case BPF_JSGT:
> - if (reg1->smin_value > sval)
> - return 1;
> - else if (reg1->smax_value <= sval)
> - return 0;
> - break;
> - case BPF_JLT:
> - if (reg1->umax_value < val)
> - return 1;
> - else if (reg1->umin_value >= val)
> - return 0;
> - break;
> - case BPF_JSLT:
> - if (reg1->smax_value < sval)
> - return 1;
> - else if (reg1->smin_value >= sval)
> - return 0;
> - break;
> - case BPF_JGE:
> - if (reg1->umin_value >= val)
> - return 1;
> - else if (reg1->umax_value < val)
> - return 0;
> - break;
> - case BPF_JSGE:
> - if (reg1->smin_value >= sval)
> - return 1;
> - else if (reg1->smax_value < sval)
> - return 0;
> - break;
> - case BPF_JLE:
> - if (reg1->umax_value <= val)
> - return 1;
> - else if (reg1->umin_value > val)
> - return 0;
> - break;
> - case BPF_JSLE:
> - if (reg1->smax_value <= sval)
> - return 1;
> - else if (reg1->smin_value > sval)
> + else if (smin1 > sval)
> return 0;
> break;
> }
> @@ -14458,9 +14378,7 @@ static int is_branch_taken(struct bpf_reg_state *reg1, struct bpf_reg_state *reg
> }
> }
>
> - if (is_jmp32)
> - return is_branch32_taken(reg1, reg2, opcode);
> - return is_branch64_taken(reg1, reg2, opcode);
> + return is_scalar_branch_taken(reg1, reg2, opcode, is_jmp32);
> }
>
> /* Adjusts the register min/max values in the case that the dst_reg is the