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bpf: simplify verifier register state assignments 

verifier is using the following structure to track the state of registers:
struct reg_state {
    enum bpf_reg_type type;
    union {
        int imm;
        struct bpf_map *map_ptr;
    };
};
and later on in states_equal() does memcmp(&old->regs[i], &cur->regs[i],..)
to find equivalent states.
Throughout the code of verifier there are assignements to 'imm' and 'map_ptr'
fields and it's not obvious that most of the assignments into 'imm' don't
need to clear extra 4 bytes (like mark_reg_unknown_value() does) to make sure
that memcmp doesn't go over junk left from 'map_ptr' assignment.

Simplify the code by converting 'int' into 'long'

Suggested-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Alexei Starovoitov 2016-04-06 19:39:21 -07:00 committed by David S. Miller
parent ae95d71261
commit 4923ec0b10
1 changed files with 2 additions and 4 deletions
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6
kernel/bpf/verifier.c
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@ -142,7 +142,7 @@ struct reg_state {
enum bpf_reg_type type;
union {
/* valid when type == CONST_IMM | PTR_TO_STACK */
int imm;
long imm;
/* valid when type == CONST_PTR_TO_MAP | PTR_TO_MAP_VALUE |
* PTR_TO_MAP_VALUE_OR_NULL
@ -263,7 +263,7 @@ static void print_verifier_state(struct verifier_env *env)
continue;
verbose(" R%d=%s", i, reg_type_str[t]);
if (t == CONST_IMM || t == PTR_TO_STACK)
verbose("%d", env->cur_state.regs[i].imm);
verbose("%ld", env->cur_state.regs[i].imm);
else if (t == CONST_PTR_TO_MAP || t == PTR_TO_MAP_VALUE ||
t == PTR_TO_MAP_VALUE_OR_NULL)
verbose("(ks=%d,vs=%d)",
@ -480,7 +480,6 @@ static void init_reg_state(struct reg_state *regs)
for (i = 0; i < MAX_BPF_REG; i++) {
regs[i].type = NOT_INIT;
regs[i].imm = 0;
regs[i].map_ptr = NULL;
}
/* frame pointer */
@ -495,7 +494,6 @@ static void mark_reg_unknown_value(struct reg_state *regs, u32 regno)
BUG_ON(regno >= MAX_BPF_REG);
regs[regno].type = UNKNOWN_VALUE;
regs[regno].imm = 0;
regs[regno].map_ptr = NULL;
}
enum reg_arg_type {