On Sun, Apr 28, 2024 at 8:15 AM Xu Kuohai <xukuohai@xxxxxxxxxxxxxxx> wrote: > > On 4/27/2024 4:36 AM, Andrii Nakryiko wrote: > > 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 > > > > OK, will update the align style > > >> + 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? > > > > Totally agree, the AND of any set with the range [-1,0] is equivalent > to adding number 0 to the set! > > Based on this observation, I've rewritten the patch as follows. > > diff --git a/include/linux/tnum.h b/include/linux/tnum.h > index 3c13240077b8..5e795d728b9f 100644 > --- a/include/linux/tnum.h > +++ b/include/linux/tnum.h > @@ -52,6 +52,9 @@ struct tnum tnum_mul(struct tnum a, struct tnum b); > /* Return a tnum representing numbers satisfying both @a and @b */ > struct tnum tnum_intersect(struct tnum a, struct tnum b); > > +/* Return a tnum representing numbers satisfying either @a or @b */ > +struct tnum tnum_union(struct tnum a, struct tnum b); > + > /* Return @a with all but the lowest @size bytes cleared */ > struct tnum tnum_cast(struct tnum a, u8 size); > > diff --git a/kernel/bpf/tnum.c b/kernel/bpf/tnum.c > index 9dbc31b25e3d..9d4480a683ca 100644 > --- a/kernel/bpf/tnum.c > +++ b/kernel/bpf/tnum.c > @@ -150,6 +150,29 @@ struct tnum tnum_intersect(struct tnum a, struct tnum b) > return TNUM(v & ~mu, mu); > } > > +/* > + * Each bit has 3 states: unkown, known 0, known 1. If using x to represent > + * unknown state, the result of the union of two bits is as follows: > + * > + * | x 0 1 > + * -----+------------ > + * x | x x x > + * 0 | x 0 x > + * 1 | x x 1 > + * > + * For tnum a and b, only the bits that are both known 0 or known 1 in a > + * and b are known in the result of union a and b. > + */ > +struct tnum tnum_union(struct tnum a, struct tnum b) > +{ > + u64 v0, v1, mu; > + > + mu = a.mask | b.mask; // unkown bits either in a or b > + v1 = (a.value & b.value) & ~mu; // "known 1" bits in both a and b > + v0 = (~a.value & ~b.value) & ~mu; // "known 0" bits in both a and b no C++-style comments, please > + return TNUM(v1, mu | ~(v0 | v1)); > +} > + I've CC'ed Edward, hopefully he can take a look as well. Please CC him on future patches touching tnum as well. > struct tnum tnum_cast(struct tnum a, u8 size) > { > a.value &= (1ULL << (size * 8)) - 1; > { > a.value &= (1ULL << (size * 8)) - 1; > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c > index 8f0f2e21699e..b69c89bc5cfc 100644 > --- a/kernel/bpf/verifier.c > +++ b/kernel/bpf/verifier.c > @@ -13478,6 +13478,28 @@ static void scalar32_min_max_and(struct bpf_reg_state *dst_reg, > return; > } > > + /* Special case: dst_reg is in range [-1, 0] */ > + if (dst_reg->s32_min_value == -1 && dst_reg->s32_max_value == 0) { > + var32_off = tnum_union(src_reg->var_off, tnum_const(0)); > + dst_reg->var_off = tnum_with_subreg(dst_reg->var_off, var32_off); > + dst_reg->u32_min_value = var32_off.value; > + dst_reg->u32_max_value = min(dst_reg->u32_max_value, umax_val); can you explain the logic behing u32 min/max updates, especially that we use completely different values for min/max and it's not clear why u32_min <= u32_max invariant will always hold. Same below > + 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_max_value, 0); > + return; > + } > + > + /* Special case: src_reg is in range [-1, 0] */ > + if (src_reg->s32_min_value == -1 && src_reg->s32_max_value == 0) { > + var32_off = tnum_union(dst_reg->var_off, tnum_const(0)); > + dst_reg->var_off = tnum_with_subreg(dst_reg->var_off, var32_off); > + dst_reg->u32_min_value = var32_off.value; > + dst_reg->u32_max_value = min(dst_reg->u32_max_value, umax_val); > + 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_max_value, 0); > + return; > + } > + > /* We get our minimum from the var_off, since that's inherently > * bitwise. Our maximum is the minimum of the operands' maxima. > */ > @@ -13508,6 +13530,26 @@ static void scalar_min_max_and(struct bpf_reg_state *dst_reg, > return; > } > > + /* Special case: dst_reg is in range [-1, 0] */ > + if (dst_reg->smin_value == -1 && dst_reg->smax_value == 0) { > + dst_reg->var_off = tnum_union(src_reg->var_off, tnum_const(0)); > + dst_reg->umin_value = dst_reg->var_off.value; > + dst_reg->umax_value = min(dst_reg->umax_value, umax_val); > + dst_reg->smin_value = min_t(s64, src_reg->smin_value, 0); > + dst_reg->smax_value = max_t(s64, src_reg->smax_value, 0); > + return; > + } > + > + /* Special case: src_reg is in range [-1, 0] */ > + if (src_reg->smin_value == -1 && src_reg->smax_value == 0) { > + dst_reg->var_off = tnum_union(dst_reg->var_off, tnum_const(0)); > + dst_reg->umin_value = dst_reg->var_off.value; > + dst_reg->umax_value = min(dst_reg->umax_value, umax_val); > + dst_reg->smin_value = min_t(s64, dst_reg->smin_value, 0); > + dst_reg->smax_value = max_t(s64, dst_reg->smax_value, 0); > + return; > + } > + > > >> + 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. > >> */ > > > > [...] > > >
