On Tue, Apr 23, 2024 at 7:26 PM Xu Kuohai <xukuohai@xxxxxxxxxxxxxxx> wrote: > > On 4/24/2024 5:55 AM, Yonghong Song wrote: > > > > On 4/20/24 1:33 AM, Xu Kuohai wrote: > >> On 4/20/2024 7:00 AM, Eduard Zingerman wrote: > >>> On Thu, 2024-04-11 at 20:27 +0800, Xu Kuohai wrote: > >>>> From: Xu Kuohai <xukuohai@xxxxxxxxxx> > >>>> > >>>> With lsm return value check, the no-alu32 version test_libbpf_get_fd_by_id_opts > >>>> is rejected by the verifier, and the log says: > >>>> > >>>> 0: R1=ctx() R10=fp0 > >>>> ; int BPF_PROG(check_access, struct bpf_map *map, fmode_t fmode) @ test_libbpf_get_fd_by_id_opts.c:27 > >>>> 0: (b7) r0 = 0 ; R0_w=0 > >>>> 1: (79) r2 = *(u64 *)(r1 +0) > >>>> func 'bpf_lsm_bpf_map' arg0 has btf_id 916 type STRUCT 'bpf_map' > >>>> 2: R1=ctx() R2_w=trusted_ptr_bpf_map() > >>>> ; if (map != (struct bpf_map *)&data_input) @ test_libbpf_get_fd_by_id_opts.c:29 > >>>> 2: (18) r3 = 0xffff9742c0951a00 ; R3_w=map_ptr(map=data_input,ks=4,vs=4) > >>>> 4: (5d) if r2 != r3 goto pc+4 ; R2_w=trusted_ptr_bpf_map() R3_w=map_ptr(map=data_input,ks=4,vs=4) > >>>> ; int BPF_PROG(check_access, struct bpf_map *map, fmode_t fmode) @ test_libbpf_get_fd_by_id_opts.c:27 > >>>> 5: (79) r0 = *(u64 *)(r1 +8) ; R0_w=scalar() R1=ctx() > >>>> ; if (fmode & FMODE_WRITE) @ test_libbpf_get_fd_by_id_opts.c:32 > >>>> 6: (67) r0 <<= 62 ; R0_w=scalar(smax=0x4000000000000000,umax=0xc000000000000000,smin32=0,smax32=umax32=0,var_off=(0x0; 0xc000000000000000)) > >>>> 7: (c7) r0 s>>= 63 ; R0_w=scalar(smin=smin32=-1,smax=smax32=0) > >>>> ; @ test_libbpf_get_fd_by_id_opts.c:0 > >>>> 8: (57) r0 &= -13 ; R0_w=scalar(smax=0x7ffffffffffffff3,umax=0xfffffffffffffff3,smax32=0x7ffffff3,umax32=0xfffffff3,var_off=(0x0; 0xfffffffffffffff3)) > >>>> ; int BPF_PROG(check_access, struct bpf_map *map, fmode_t fmode) @ test_libbpf_get_fd_by_id_opts.c:27 > >>>> 9: (95) exit [...] > > As suggested by Eduard, this patch makes a special case for source > or destination register of '&=' operation being in range [-1, 0]. > > Meaning that one of the '&=' operands is either: > - all ones, in which case the counterpart is the result of the operation; > - all zeros, in which case zero is the result of the operation. > > And MIN and MAX values could be derived based on above two observations. > > [0] https://lore.kernel.org/bpf/e62e2971301ca7f2e9eb74fc500c520285cad8f5.camel@xxxxxxxxx/ > [1] https://github.com/llvm/llvm-project/blob/4523a267829c807f3fc8fab8e5e9613985a51565/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp > > Suggested-by: Eduard Zingerman <eddyz87@xxxxxxxxx> > Signed-off-by: Xu Kuohai <xukuohai@xxxxxxxxxx> > > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c > index 640747b53745..30c551d39329 100644 > --- a/kernel/bpf/verifier.c > +++ b/kernel/bpf/verifier.c > @@ -13374,6 +13374,24 @@ static void scalar32_min_max_and(struct bpf_reg_state *dst_reg, > dst_reg->u32_min_value = var32_off.value; > dst_reg->u32_max_value = min(dst_reg->u32_max_value, umax_val); > > + /* Special case: src_reg is known and dst_reg is in range [-1, 0] */ > + if (src_known && > + dst_reg->s32_min_value == -1 && dst_reg->s32_max_value == 0 && > + dst_reg->smin_value == -1 && dst_reg->smax_value == 0) { please keep if () condition aligned across multiple lines, it's super confusing this way > + dst_reg->s32_min_value = min_t(s32, src_reg->s32_min_value, 0); > + dst_reg->s32_max_value = max_t(s32, src_reg->s32_min_value, 0); do we need to update tnum parts as well (or reset and re-derive, probably)? btw, can't we support src being a range here? the idea is that dst_reg either all ones or all zeros. For and it means that it either stays all zero, or will be *exactly equal* to src, right? So I think the logic would be: a) if [s32_min, s32_max] is on the same side of zero, then resulting range would be [min(s32_min, 0), max(s32_max, 0)], just like you have here b) if [s32_min, s32_max] contains zero, then resulting range will be exactly [s32_min, s32_max] Or did I make a mistake above? > + return; > + } > + > + /* Special case: dst_reg is known and src_reg is in range [-1, 0] */ > + if (dst_known && > + src_reg->s32_min_value == -1 && src_reg->s32_max_value == 0 && > + src_reg->smin_value == -1 && src_reg->smax_value == 0) { > + dst_reg->s32_min_value = min_t(s32, dst_reg->s32_min_value, 0); > + dst_reg->s32_max_value = max_t(s32, dst_reg->s32_min_value, 0); > + return; > + } > + > /* Safe to set s32 bounds by casting u32 result into s32 when u32 > * doesn't cross sign boundary. Otherwise set s32 bounds to unbounded. > */ [...]
