system/linux
system/linux
1
0
Fork 0
mirror of https://github.com/torvalds/linux synced 2024-09-06 18:01:05 +00:00
Code Issues Packages Projects Releases Wiki Activity

bpf: generalize is_branch_taken to handle all conditional jumps in one place

Browse source 
Make is_branch_taken() a single entry point for branch pruning decision
making, handling both pointer vs pointer, pointer vs scalar, and scalar
vs scalar cases in one place. This also nicely cleans up check_cond_jmp_op().

Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/r/20231102033759.2541186-15-andrii@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Andrii Nakryiko 2023-11-01 20:37:56 -07:00 committed by Alexei Starovoitov
parent c697289efe
commit b74c2a842b
1 changed files with 25 additions and 24 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

49
kernel/bpf/verifier.c
View file

@ -14188,6 +14188,19 @@ static void find_good_pkt_pointers(struct bpf_verifier_state *vstate,
}));
}
/* check if register is a constant scalar value */
static bool is_reg_const(struct bpf_reg_state *reg, bool subreg32)
{
return reg->type == SCALAR_VALUE &&
tnum_is_const(subreg32 ? tnum_subreg(reg->var_off) : reg->var_off);
}
/* assuming is_reg_const() is true, return constant value of a register */
static u64 reg_const_value(struct bpf_reg_state *reg, bool subreg32)
{
return subreg32 ? tnum_subreg(reg->var_off).value : reg->var_off.value;
}
/*
* <reg1> <op> <reg2>, currently assuming reg2 is a constant
*/
@ -14429,12 +14442,20 @@ static int is_pkt_ptr_branch_taken(struct bpf_reg_state *dst_reg,
static int is_branch_taken(struct bpf_reg_state *reg1, struct bpf_reg_state *reg2,
u8 opcode, bool is_jmp32)
{
struct tnum reg2_tnum = is_jmp32 ? tnum_subreg(reg2->var_off) : reg2->var_off;
u64 val;
if (!tnum_is_const(reg2_tnum))
if (reg_is_pkt_pointer_any(reg1) && reg_is_pkt_pointer_any(reg2) && !is_jmp32)
return is_pkt_ptr_branch_taken(reg1, reg2, opcode);
/* try to make sure reg2 is a constant SCALAR_VALUE */
if (!is_reg_const(reg2, is_jmp32)) {
opcode = flip_opcode(opcode);
swap(reg1, reg2);
}
/* for now we expect reg2 to be a constant to make any useful decisions */
if (!is_reg_const(reg2, is_jmp32))
return -1;
val = reg2_tnum.value;
val = reg_const_value(reg2, is_jmp32);
if (__is_pointer_value(false, reg1)) {
if (!reg_not_null(reg1))
@ -14915,27 +14936,7 @@ static int check_cond_jmp_op(struct bpf_verifier_env *env,
}
is_jmp32 = BPF_CLASS(insn->code) == BPF_JMP32;
if (BPF_SRC(insn->code) == BPF_K) {
pred = is_branch_taken(dst_reg, src_reg, opcode, is_jmp32);
} else if (src_reg->type == SCALAR_VALUE &&
is_jmp32 && tnum_is_const(tnum_subreg(src_reg->var_off))) {
pred = is_branch_taken(dst_reg, src_reg, opcode, is_jmp32);
} else if (src_reg->type == SCALAR_VALUE &&
!is_jmp32 && tnum_is_const(src_reg->var_off)) {
pred = is_branch_taken(dst_reg, src_reg, opcode, is_jmp32);
} else if (dst_reg->type == SCALAR_VALUE &&
is_jmp32 && tnum_is_const(tnum_subreg(dst_reg->var_off))) {
pred = is_branch_taken(src_reg, dst_reg, flip_opcode(opcode), is_jmp32);
} else if (dst_reg->type == SCALAR_VALUE &&
!is_jmp32 && tnum_is_const(dst_reg->var_off)) {
pred = is_branch_taken(src_reg, dst_reg, flip_opcode(opcode), is_jmp32);
} else if (reg_is_pkt_pointer_any(dst_reg) &&
reg_is_pkt_pointer_any(src_reg) &&
!is_jmp32) {
pred = is_pkt_ptr_branch_taken(dst_reg, src_reg, opcode);
}
pred = is_branch_taken(dst_reg, src_reg, opcode, is_jmp32);
if (pred >= 0) {
/* If we get here with a dst_reg pointer type it is because
* above is_branch_taken() special cased the 0 comparison.