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bpf: Add flags arg to bpf_dynptr_read and bpf_dynptr_write APIs
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Commit 13bbbfb ("bpf: Add bpf_dynptr_read and bpf_dynptr_write")
added the bpf_dynptr_write() and bpf_dynptr_read() APIs.

However, it will be needed for some dynptr types to pass in flags as
well (e.g. when writing to a skb, the user may like to invalidate the
hash or recompute the checksum).

This patch adds a "u64 flags" arg to the bpf_dynptr_read() and
bpf_dynptr_write() APIs before their UAPI signature freezes where
we then cannot change them anymore with a 5.19.x released kernel.

Fixes: 13bbbfb ("bpf: Add bpf_dynptr_read and bpf_dynptr_write")
Signed-off-by: Joanne Koong <joannelkoong@gmail.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/r/20220706232547.4016651-1-joannelkoong@gmail.com
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@joannekoong @borkmann
joannekoong authored and borkmann committed Jul 8, 2022
1 parent 0326195 commit f8d3da4
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Showing 5 changed files with 29 additions and 19 deletions.
11 changes: 7 additions & 4 deletions include/uapi/linux/bpf.h
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Original file line number Diff line number Diff line change
Expand Up @@ -5222,22 +5222,25 @@ union bpf_attr {
* Return
* Nothing. Always succeeds.
*
* long bpf_dynptr_read(void *dst, u32 len, struct bpf_dynptr *src, u32 offset)
* long bpf_dynptr_read(void *dst, u32 len, struct bpf_dynptr *src, u32 offset, u64 flags)
* Description
* Read *len* bytes from *src* into *dst*, starting from *offset*
* into *src*.
* *flags* is currently unused.
* Return
* 0 on success, -E2BIG if *offset* + *len* exceeds the length
* of *src*'s data, -EINVAL if *src* is an invalid dynptr.
* of *src*'s data, -EINVAL if *src* is an invalid dynptr or if
* *flags* is not 0.
*
* long bpf_dynptr_write(struct bpf_dynptr *dst, u32 offset, void *src, u32 len)
* long bpf_dynptr_write(struct bpf_dynptr *dst, u32 offset, void *src, u32 len, u64 flags)
* Description
* Write *len* bytes from *src* into *dst*, starting from *offset*
* into *dst*.
* *flags* is currently unused.
* Return
* 0 on success, -E2BIG if *offset* + *len* exceeds the length
* of *dst*'s data, -EINVAL if *dst* is an invalid dynptr or if *dst*
* is a read-only dynptr.
* is a read-only dynptr or if *flags* is not 0.
*
* void *bpf_dynptr_data(struct bpf_dynptr *ptr, u32 offset, u32 len)
* Description
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12 changes: 8 additions & 4 deletions kernel/bpf/helpers.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1497,11 +1497,12 @@ const struct bpf_func_proto bpf_dynptr_from_mem_proto = {
.arg4_type = ARG_PTR_TO_DYNPTR | DYNPTR_TYPE_LOCAL | MEM_UNINIT,
};

BPF_CALL_4(bpf_dynptr_read, void *, dst, u32, len, struct bpf_dynptr_kern *, src, u32, offset)
BPF_CALL_5(bpf_dynptr_read, void *, dst, u32, len, struct bpf_dynptr_kern *, src,
u32, offset, u64, flags)
{
int err;

if (!src->data)
if (!src->data || flags)
return -EINVAL;

err = bpf_dynptr_check_off_len(src, offset, len);
Expand All @@ -1521,13 +1522,15 @@ const struct bpf_func_proto bpf_dynptr_read_proto = {
.arg2_type = ARG_CONST_SIZE_OR_ZERO,
.arg3_type = ARG_PTR_TO_DYNPTR,
.arg4_type = ARG_ANYTHING,
.arg5_type = ARG_ANYTHING,
};

BPF_CALL_4(bpf_dynptr_write, struct bpf_dynptr_kern *, dst, u32, offset, void *, src, u32, len)
BPF_CALL_5(bpf_dynptr_write, struct bpf_dynptr_kern *, dst, u32, offset, void *, src,
u32, len, u64, flags)
{
int err;

if (!dst->data || bpf_dynptr_is_rdonly(dst))
if (!dst->data || flags || bpf_dynptr_is_rdonly(dst))
return -EINVAL;

err = bpf_dynptr_check_off_len(dst, offset, len);
Expand All @@ -1547,6 +1550,7 @@ const struct bpf_func_proto bpf_dynptr_write_proto = {
.arg2_type = ARG_ANYTHING,
.arg3_type = ARG_PTR_TO_MEM | MEM_RDONLY,
.arg4_type = ARG_CONST_SIZE_OR_ZERO,
.arg5_type = ARG_ANYTHING,
};

BPF_CALL_3(bpf_dynptr_data, struct bpf_dynptr_kern *, ptr, u32, offset, u32, len)
Expand Down
11 changes: 7 additions & 4 deletions tools/include/uapi/linux/bpf.h
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Original file line number Diff line number Diff line change
Expand Up @@ -5222,22 +5222,25 @@ union bpf_attr {
* Return
* Nothing. Always succeeds.
*
* long bpf_dynptr_read(void *dst, u32 len, struct bpf_dynptr *src, u32 offset)
* long bpf_dynptr_read(void *dst, u32 len, struct bpf_dynptr *src, u32 offset, u64 flags)
* Description
* Read *len* bytes from *src* into *dst*, starting from *offset*
* into *src*.
* *flags* is currently unused.
* Return
* 0 on success, -E2BIG if *offset* + *len* exceeds the length
* of *src*'s data, -EINVAL if *src* is an invalid dynptr.
* of *src*'s data, -EINVAL if *src* is an invalid dynptr or if
* *flags* is not 0.
*
* long bpf_dynptr_write(struct bpf_dynptr *dst, u32 offset, void *src, u32 len)
* long bpf_dynptr_write(struct bpf_dynptr *dst, u32 offset, void *src, u32 len, u64 flags)
* Description
* Write *len* bytes from *src* into *dst*, starting from *offset*
* into *dst*.
* *flags* is currently unused.
* Return
* 0 on success, -E2BIG if *offset* + *len* exceeds the length
* of *dst*'s data, -EINVAL if *dst* is an invalid dynptr or if *dst*
* is a read-only dynptr.
* is a read-only dynptr or if *flags* is not 0.
*
* void *bpf_dynptr_data(struct bpf_dynptr *ptr, u32 offset, u32 len)
* Description
Expand Down
10 changes: 5 additions & 5 deletions tools/testing/selftests/bpf/progs/dynptr_fail.c
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Original file line number Diff line number Diff line change
Expand Up @@ -140,12 +140,12 @@ int use_after_invalid(void *ctx)

bpf_ringbuf_reserve_dynptr(&ringbuf, sizeof(read_data), 0, &ptr);

bpf_dynptr_read(read_data, sizeof(read_data), &ptr, 0);
bpf_dynptr_read(read_data, sizeof(read_data), &ptr, 0, 0);

bpf_ringbuf_submit_dynptr(&ptr, 0);

/* this should fail */
bpf_dynptr_read(read_data, sizeof(read_data), &ptr, 0);
bpf_dynptr_read(read_data, sizeof(read_data), &ptr, 0, 0);

return 0;
}
Expand Down Expand Up @@ -338,7 +338,7 @@ int invalid_helper2(void *ctx)
get_map_val_dynptr(&ptr);

/* this should fail */
bpf_dynptr_read(read_data, sizeof(read_data), (void *)&ptr + 8, 0);
bpf_dynptr_read(read_data, sizeof(read_data), (void *)&ptr + 8, 0, 0);

return 0;
}
Expand Down Expand Up @@ -377,7 +377,7 @@ int invalid_write2(void *ctx)
memcpy((void *)&ptr + 8, &x, sizeof(x));

/* this should fail */
bpf_dynptr_read(read_data, sizeof(read_data), &ptr, 0);
bpf_dynptr_read(read_data, sizeof(read_data), &ptr, 0, 0);

bpf_ringbuf_submit_dynptr(&ptr, 0);

Expand Down Expand Up @@ -473,7 +473,7 @@ int invalid_read2(void *ctx)
get_map_val_dynptr(&ptr);

/* this should fail */
bpf_dynptr_read(read_data, sizeof(read_data), (void *)&ptr + 1, 0);
bpf_dynptr_read(read_data, sizeof(read_data), (void *)&ptr + 1, 0, 0);

return 0;
}
Expand Down
4 changes: 2 additions & 2 deletions tools/testing/selftests/bpf/progs/dynptr_success.c
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Original file line number Diff line number Diff line change
Expand Up @@ -43,10 +43,10 @@ int test_read_write(void *ctx)
bpf_ringbuf_reserve_dynptr(&ringbuf, sizeof(write_data), 0, &ptr);

/* Write data into the dynptr */
err = err ?: bpf_dynptr_write(&ptr, 0, write_data, sizeof(write_data));
err = bpf_dynptr_write(&ptr, 0, write_data, sizeof(write_data), 0);

/* Read the data that was written into the dynptr */
err = err ?: bpf_dynptr_read(read_data, sizeof(read_data), &ptr, 0);
err = err ?: bpf_dynptr_read(read_data, sizeof(read_data), &ptr, 0, 0);

/* Ensure the data we read matches the data we wrote */
for (i = 0; i < sizeof(read_data); i++) {
Expand Down

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