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bpf: Fix attaching fentry/fexit/fmod_ret/lsm to modules

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This resolves two problems with attachment of fentry/fexit/fmod_ret/lsm
to functions located in modules:

1. The verifier tries to find the address to attach to in kallsyms. This
   is always done by searching the entire kallsyms, not respecting the
   module in which the function is located. Such approach causes an
   incorrect attachment address to be computed if the function to attach
   to is shadowed by a function of the same name located earlier in
   kallsyms.

2. If the address to attach to is located in a module, the module
   reference is only acquired in register_fentry. If the module is
   unloaded between the place where the address is found
   (bpf_check_attach_target in the verifier) and register_fentry, it is
   possible that another module is loaded to the same address which may
   lead to potential errors.

Since the attachment must contain the BTF of the program to attach to,
we extract the module from it and search for the function address in the
correct module (resolving problem no. 1). Then, the module reference is
taken directly in bpf_check_attach_target and stored in the bpf program
(in bpf_prog_aux). The reference is only released when the program is
unloaded (resolving problem no. 2).

Signed-off-by: Viktor Malik <vmalik@redhat.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Reviewed-by: Luis Chamberlain <mcgrof@kernel.org>
Link: https://lore.kernel.org/r/3f6a9d8ae850532b5ef864ef16327b0f7a669063.1678432753.git.vmalik@redhat.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Viktor Malik 2023-03-10 08:40:59 +01:00 • committed by Alexei Starovoitov
parent b8a2e3f93d
commit 31bf1dbccf
5 changed files with 30 additions and 29 deletions
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2
include/linux/bpf.h
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@ -1103,6 +1103,7 @@ struct bpf_trampoline {
struct bpf_attach_target_info {
struct btf_func_model fmodel;
long tgt_addr;
struct module *tgt_mod;
const char *tgt_name;
const struct btf_type *tgt_type;
};
@ -1406,6 +1407,7 @@ struct bpf_prog_aux {
* main prog always has linfo_idx == 0
*/
u32 linfo_idx;
struct module *mod;
u32 num_exentries;
struct exception_table_entry *extable;
union {