On Fri, Feb 17, 2023 at 1:06 AM Jiri Olsa <olsajiri@xxxxxxxxx> wrote:
>
> On Thu, Feb 16, 2023 at 04:54:51PM -0800, Joanne Koong wrote:
> > This change refactors check_mem_access() to check against the base type of
> > the register, and uses switch case checking instead of if / else if
> > checks. This change also uses the existing clear_called_saved_regs()
> > function for resetting caller saved regs in check_helper_call().
> >
> > Signed-off-by: Joanne Koong <joannelkoong@xxxxxxxxx>
> > ---
> > kernel/bpf/verifier.c | 67 +++++++++++++++++++++++++++++--------------
> > 1 file changed, 46 insertions(+), 21 deletions(-)
> >
> > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> > index 272563a0b770..b40165be2943 100644
> > --- a/kernel/bpf/verifier.c
> > +++ b/kernel/bpf/verifier.c
> > @@ -5317,7 +5317,8 @@ static int check_mem_access(struct bpf_verifier_env *env, int insn_idx, u32 regn
> > /* for access checks, reg->off is just part of off */
> > off += reg->off;
> >
> > - if (reg->type == PTR_TO_MAP_KEY) {
> > + switch (base_type(reg->type)) {
> > + case PTR_TO_MAP_KEY:
> > if (t == BPF_WRITE) {
> > verbose(env, "write to change key R%d not allowed\n", regno);
> > return -EACCES;
> > @@ -5329,7 +5330,10 @@ static int check_mem_access(struct bpf_verifier_env *env, int insn_idx, u32 regn
> > return err;
> > if (value_regno >= 0)
> > mark_reg_unknown(env, regs, value_regno);
> > - } else if (reg->type == PTR_TO_MAP_VALUE) {
> > +
> > + break;
> > + case PTR_TO_MAP_VALUE:
> > + {
>
> I'm getting failure in this test:
> #92/1 jeq_infer_not_null/jeq_infer_not_null_ptr_to_btfid:FAIL
>
> I wonder with this change we execute this case even if there's PTR_MAYBE_NULL set,
> which we did not do before, so the test won't fail now as expected
Thanks for reviewing this, I will investigate this test failure!
>
> > struct btf_field *kptr_field = NULL;
> >
> > if (t == BPF_WRITE && value_regno >= 0 &&
> > @@ -5369,7 +5373,10 @@ static int check_mem_access(struct bpf_verifier_env *env, int insn_idx, u32 regn
> > mark_reg_unknown(env, regs, value_regno);
> > }
> > }
> > - } else if (base_type(reg->type) == PTR_TO_MEM) {
> > + break;
> > + }
>
> SNIP
>
> > @@ -5521,7 +5539,17 @@ static int check_mem_access(struct bpf_verifier_env *env, int insn_idx, u32 regn
> >
> > if (!err && value_regno >= 0 && (rdonly_mem || t == BPF_READ))
> > mark_reg_unknown(env, regs, value_regno);
> > - } else {
> > + break;
> > + }
> > + case PTR_TO_BTF_ID:
> > + if (!type_may_be_null(reg->type)) {
> > + err = check_ptr_to_btf_access(env, regs, regno, off, size, t,
> > + value_regno);
> > + break;
> > + } else {
> > + fallthrough;
> > + }
>
> nit, no need for the else branch, just use fallthrough directly
>
> > + default:
> > verbose(env, "R%d invalid mem access '%s'\n", regno,
> > reg_type_str(env, reg->type));
> > return -EACCES;
> > @@ -8377,10 +8405,7 @@ static int check_helper_call(struct bpf_verifier_env *env, struct bpf_insn *insn
> > return err;
> >
> > /* reset caller saved regs */
>
> nit, we could remove the comment as well, the function name says it all
>
> jirka
>
> > - for (i = 0; i < CALLER_SAVED_REGS; i++) {
> > - mark_reg_not_init(env, regs, caller_saved[i]);
> > - check_reg_arg(env, caller_saved[i], DST_OP_NO_MARK);
> > - }
> > + clear_caller_saved_regs(env, regs);
> >
> > /* helper call returns 64-bit value. */
> > regs[BPF_REG_0].subreg_def = DEF_NOT_SUBREG;
> > --
> > 2.30.2
> >
