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bpf: return long from bpf_map_ops funcs

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This patch changes the return types of bpf_map_ops functions to long, where
previously int was returned. Using long allows for bpf programs to maintain
the sign bit in the absence of sign extension during situations where
inlined bpf helper funcs make calls to the bpf_map_ops funcs and a negative
error is returned.

The definitions of the helper funcs are generated from comments in the bpf
uapi header at `include/uapi/linux/bpf.h`. The return type of these
helpers was previously changed from int to long in commit bdb7b79b4c. For
any case where one of the map helpers call the bpf_map_ops funcs that are
still returning 32-bit int, a compiler might not include sign extension
instructions to properly convert the 32-bit negative value a 64-bit
negative value.

For example:
bpf assembly excerpt of an inlined helper calling a kernel function and
checking for a specific error:

; err = bpf_map_update_elem(&mymap, &key, &val, BPF_NOEXIST);
  ...
  46:	call   0xffffffffe103291c	; htab_map_update_elem
; if (err && err != -EEXIST) {
  4b:	cmp    $0xffffffffffffffef,%rax ; cmp -EEXIST,%rax

kernel function assembly excerpt of return value from
`htab_map_update_elem` returning 32-bit int:

movl $0xffffffef, %r9d
...
movl %r9d, %eax

...results in the comparison:
cmp $0xffffffffffffffef, $0x00000000ffffffef

Fixes: bdb7b79b4c ("bpf: Switch most helper return values from 32-bit int to 64-bit long")
Tested-by: Eduard Zingerman <eddyz87@gmail.com>
Signed-off-by: JP Kobryn <inwardvessel@gmail.com>
Link: https://lore.kernel.org/r/20230322194754.185781-3-inwardvessel@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
JP Kobryn 2023-03-22 12:47:54 -07:00 • committed by Alexei Starovoitov
parent 830154cdc5
commit d7ba4cc900
21 changed files with 110 additions and 110 deletions
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14
include/linux/bpf.h
View file

@ -96,11 +96,11 @@ struct bpf_map_ops {
/* funcs callable from userspace and from eBPF programs */
void *(*map_lookup_elem)(struct bpf_map *map, void *key);
int (*map_update_elem)(struct bpf_map *map, void *key, void *value, u64 flags);
int (*map_delete_elem)(struct bpf_map *map, void *key);
int (*map_push_elem)(struct bpf_map *map, void *value, u64 flags);
int (*map_pop_elem)(struct bpf_map *map, void *value);
int (*map_peek_elem)(struct bpf_map *map, void *value);
long (*map_update_elem)(struct bpf_map *map, void *key, void *value, u64 flags);
long (*map_delete_elem)(struct bpf_map *map, void *key);
long (*map_push_elem)(struct bpf_map *map, void *value, u64 flags);
long (*map_pop_elem)(struct bpf_map *map, void *value);
long (*map_peek_elem)(struct bpf_map *map, void *value);
void *(*map_lookup_percpu_elem)(struct bpf_map *map, void *key, u32 cpu);
/* funcs called by prog_array and perf_event_array map */
@ -139,7 +139,7 @@ struct bpf_map_ops {
struct bpf_local_storage __rcu ** (*map_owner_storage_ptr)(void *owner);
/* Misc helpers.*/
int (*map_redirect)(struct bpf_map *map, u64 key, u64 flags);
long (*map_redirect)(struct bpf_map *map, u64 key, u64 flags);
/* map_meta_equal must be implemented for maps that can be
* used as an inner map. It is a runtime check to ensure
@ -157,7 +157,7 @@ struct bpf_map_ops {
int (*map_set_for_each_callback_args)(struct bpf_verifier_env *env,
struct bpf_func_state *caller,
struct bpf_func_state *callee);
int (*map_for_each_callback)(struct bpf_map *map,
long (*map_for_each_callback)(struct bpf_map *map,
bpf_callback_t callback_fn,
void *callback_ctx, u64 flags);