On Sat, Dec 20, 2025 at 3:35 AM Zesen Liu <[email protected]> wrote: > > After commit 37cce22dbd51 ("bpf: verifier: Refactor helper access type > tracking"), > the verifier started relying on the access type tags in helper > function prototypes to perform memory access optimizations. > > Currently, several helper functions utilizing ARG_PTR_TO_MEM lack the > corresponding MEM_RDONLY or MEM_WRITE tags. This omission causes the > verifier to incorrectly assume that the buffer contents are unchanged > across the helper call. Consequently, the verifier may optimize away > subsequent reads based on this wrong assumption, leading to correctness > issues. > > Similar issues were recently addressed for specific helpers in commit > ac44dcc788b9 ("bpf: Fix verifier assumptions of bpf_d_path's output buffer") > and commit 2eb7648558a7 ("bpf: Specify access type of bpf_sysctl_get_name > args"). > > Fix these prototypes by adding the correct memory access tags. > > Fixes: 37cce22dbd51 ("bpf: verifier: Refactor helper access type tracking") > Co-developed-by: Shuran Liu <[email protected]> > Signed-off-by: Shuran Liu <[email protected]> > Co-developed-by: Peili Gao <[email protected]> > Signed-off-by: Peili Gao <[email protected]> > Co-developed-by: Haoran Ni <[email protected]> > Signed-off-by: Haoran Ni <[email protected]> > Signed-off-by: Zesen Liu <[email protected]> > --- > kernel/bpf/helpers.c | 2 +- > kernel/trace/bpf_trace.c | 6 +++--- > net/core/filter.c | 8 ++++---- > 3 files changed, 8 insertions(+), 8 deletions(-) > > diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c > index db72b96f9c8c..f66284f8ec2c 100644 > --- a/kernel/bpf/helpers.c > +++ b/kernel/bpf/helpers.c > @@ -1077,7 +1077,7 @@ const struct bpf_func_proto bpf_snprintf_proto = { > .func = bpf_snprintf, > .gpl_only = true, > .ret_type = RET_INTEGER, > - .arg1_type = ARG_PTR_TO_MEM_OR_NULL, > + .arg1_type = ARG_PTR_TO_MEM_OR_NULL | MEM_WRITE, > .arg2_type = ARG_CONST_SIZE_OR_ZERO, > .arg3_type = ARG_PTR_TO_CONST_STR, > .arg4_type = ARG_PTR_TO_MEM | PTR_MAYBE_NULL | MEM_RDONLY, > diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c > index fe28d86f7c35..59c2394981c7 100644 > --- a/kernel/trace/bpf_trace.c > +++ b/kernel/trace/bpf_trace.c > @@ -1022,7 +1022,7 @@ const struct bpf_func_proto bpf_snprintf_btf_proto = { > .func = bpf_snprintf_btf, > .gpl_only = false, > .ret_type = RET_INTEGER, > - .arg1_type = ARG_PTR_TO_MEM, > + .arg1_type = ARG_PTR_TO_MEM | MEM_WRITE, > .arg2_type = ARG_CONST_SIZE, > .arg3_type = ARG_PTR_TO_MEM | MEM_RDONLY, > .arg4_type = ARG_CONST_SIZE, > @@ -1526,7 +1526,7 @@ static const struct bpf_func_proto > bpf_read_branch_records_proto = { > .gpl_only = true, > .ret_type = RET_INTEGER, > .arg1_type = ARG_PTR_TO_CTX, > - .arg2_type = ARG_PTR_TO_MEM_OR_NULL, > + .arg2_type = ARG_PTR_TO_MEM_OR_NULL | MEM_WRITE, > .arg3_type = ARG_CONST_SIZE_OR_ZERO, > .arg4_type = ARG_ANYTHING, > }; > @@ -1661,7 +1661,7 @@ static const struct bpf_func_proto > bpf_get_stack_proto_raw_tp = { > .gpl_only = true, > .ret_type = RET_INTEGER, > .arg1_type = ARG_PTR_TO_CTX, > - .arg2_type = ARG_PTR_TO_MEM | MEM_RDONLY, > + .arg2_type = ARG_PTR_TO_UNINIT_MEM, > .arg3_type = ARG_CONST_SIZE_OR_ZERO, > .arg4_type = ARG_ANYTHING, > }; > diff --git a/net/core/filter.c b/net/core/filter.c > index 616e0520a0bb..6e07bb994aa7 100644 > --- a/net/core/filter.c > +++ b/net/core/filter.c > @@ -6399,7 +6399,7 @@ static const struct bpf_func_proto > bpf_xdp_fib_lookup_proto = { > .gpl_only = true, > .ret_type = RET_INTEGER, > .arg1_type = ARG_PTR_TO_CTX, > - .arg2_type = ARG_PTR_TO_MEM, > + .arg2_type = ARG_PTR_TO_MEM | MEM_WRITE, > .arg3_type = ARG_CONST_SIZE, > .arg4_type = ARG_ANYTHING, > }; > @@ -6454,7 +6454,7 @@ static const struct bpf_func_proto > bpf_skb_fib_lookup_proto = { > .gpl_only = true, > .ret_type = RET_INTEGER, > .arg1_type = ARG_PTR_TO_CTX, > - .arg2_type = ARG_PTR_TO_MEM, > + .arg2_type = ARG_PTR_TO_MEM | MEM_WRITE, > .arg3_type = ARG_CONST_SIZE, > .arg4_type = ARG_ANYTHING, > }; > @@ -8010,7 +8010,7 @@ static const struct bpf_func_proto > bpf_tcp_raw_gen_syncookie_ipv4_proto = { > .ret_type = RET_INTEGER, > .arg1_type = ARG_PTR_TO_FIXED_SIZE_MEM, > .arg1_size = sizeof(struct iphdr), > - .arg2_type = ARG_PTR_TO_MEM, > + .arg2_type = ARG_PTR_TO_MEM | MEM_RDONLY, > .arg3_type = ARG_CONST_SIZE_OR_ZERO, > }; > > @@ -8042,7 +8042,7 @@ static const struct bpf_func_proto > bpf_tcp_raw_gen_syncookie_ipv6_proto = { > .ret_type = RET_INTEGER, > .arg1_type = ARG_PTR_TO_FIXED_SIZE_MEM, > .arg1_size = sizeof(struct ipv6hdr), > - .arg2_type = ARG_PTR_TO_MEM, > + .arg2_type = ARG_PTR_TO_MEM | MEM_RDONLY, > .arg3_type = ARG_CONST_SIZE_OR_ZERO, > }; >
I did a quick search and there is one helper slipping. We should also annotate arg1_type of bpf_kallsyms_lookup_name with MEM_RDONLY. > > -- > 2.43.0 > >
