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Subject[PATCH 4.4 63/87] bpf: add bpf_patch_insn_single helper
Date
4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Daniel Borkmann <daniel@iogearbox.net>

commit c237ee5eb33bf19fe0591c04ff8db19da7323a83 upstream.

Move the functionality to patch instructions out of the verifier
code and into the core as the new bpf_patch_insn_single() helper
will be needed later on for blinding as well. No changes in
functionality.

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>


---
include/linux/filter.h | 3 ++
kernel/bpf/core.c | 71 +++++++++++++++++++++++++++++++++++++++++++++++++
kernel/bpf/verifier.c | 53 ++++++------------------------------
3 files changed, 83 insertions(+), 44 deletions(-)

--- a/include/linux/filter.h
+++ b/include/linux/filter.h
@@ -466,6 +466,9 @@ u64 __bpf_call_base(u64 r1, u64 r2, u64
void bpf_int_jit_compile(struct bpf_prog *fp);
bool bpf_helper_changes_skb_data(void *func);

+struct bpf_prog *bpf_patch_insn_single(struct bpf_prog *prog, u32 off,
+ const struct bpf_insn *patch, u32 len);
+
#ifdef CONFIG_BPF_JIT
typedef void (*bpf_jit_fill_hole_t)(void *area, unsigned int size);

--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -137,6 +137,77 @@ void __bpf_prog_free(struct bpf_prog *fp
}
EXPORT_SYMBOL_GPL(__bpf_prog_free);

+static bool bpf_is_jmp_and_has_target(const struct bpf_insn *insn)
+{
+ return BPF_CLASS(insn->code) == BPF_JMP &&
+ /* Call and Exit are both special jumps with no
+ * target inside the BPF instruction image.
+ */
+ BPF_OP(insn->code) != BPF_CALL &&
+ BPF_OP(insn->code) != BPF_EXIT;
+}
+
+static void bpf_adj_branches(struct bpf_prog *prog, u32 pos, u32 delta)
+{
+ struct bpf_insn *insn = prog->insnsi;
+ u32 i, insn_cnt = prog->len;
+
+ for (i = 0; i < insn_cnt; i++, insn++) {
+ if (!bpf_is_jmp_and_has_target(insn))
+ continue;
+
+ /* Adjust offset of jmps if we cross boundaries. */
+ if (i < pos && i + insn->off + 1 > pos)
+ insn->off += delta;
+ else if (i > pos + delta && i + insn->off + 1 <= pos + delta)
+ insn->off -= delta;
+ }
+}
+
+struct bpf_prog *bpf_patch_insn_single(struct bpf_prog *prog, u32 off,
+ const struct bpf_insn *patch, u32 len)
+{
+ u32 insn_adj_cnt, insn_rest, insn_delta = len - 1;
+ struct bpf_prog *prog_adj;
+
+ /* Since our patchlet doesn't expand the image, we're done. */
+ if (insn_delta == 0) {
+ memcpy(prog->insnsi + off, patch, sizeof(*patch));
+ return prog;
+ }
+
+ insn_adj_cnt = prog->len + insn_delta;
+
+ /* Several new instructions need to be inserted. Make room
+ * for them. Likely, there's no need for a new allocation as
+ * last page could have large enough tailroom.
+ */
+ prog_adj = bpf_prog_realloc(prog, bpf_prog_size(insn_adj_cnt),
+ GFP_USER);
+ if (!prog_adj)
+ return NULL;
+
+ prog_adj->len = insn_adj_cnt;
+
+ /* Patching happens in 3 steps:
+ *
+ * 1) Move over tail of insnsi from next instruction onwards,
+ * so we can patch the single target insn with one or more
+ * new ones (patching is always from 1 to n insns, n > 0).
+ * 2) Inject new instructions at the target location.
+ * 3) Adjust branch offsets if necessary.
+ */
+ insn_rest = insn_adj_cnt - off - len;
+
+ memmove(prog_adj->insnsi + off + len, prog_adj->insnsi + off + 1,
+ sizeof(*patch) * insn_rest);
+ memcpy(prog_adj->insnsi + off, patch, sizeof(*patch) * len);
+
+ bpf_adj_branches(prog_adj, off, insn_delta);
+
+ return prog_adj;
+}
+
#ifdef CONFIG_BPF_JIT
struct bpf_binary_header *
bpf_jit_binary_alloc(unsigned int proglen, u8 **image_ptr,
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -2098,26 +2098,6 @@ static void convert_pseudo_ld_imm64(stru
insn->src_reg = 0;
}

-static void adjust_branches(struct bpf_prog *prog, int pos, int delta)
-{
- struct bpf_insn *insn = prog->insnsi;
- int insn_cnt = prog->len;
- int i;
-
- for (i = 0; i < insn_cnt; i++, insn++) {
- if (BPF_CLASS(insn->code) != BPF_JMP ||
- BPF_OP(insn->code) == BPF_CALL ||
- BPF_OP(insn->code) == BPF_EXIT)
- continue;
-
- /* adjust offset of jmps if necessary */
- if (i < pos && i + insn->off + 1 > pos)
- insn->off += delta;
- else if (i > pos + delta && i + insn->off + 1 <= pos + delta)
- insn->off -= delta;
- }
-}
-
/* convert load instructions that access fields of 'struct __sk_buff'
* into sequence of instructions that access fields of 'struct sk_buff'
*/
@@ -2127,14 +2107,15 @@ static int convert_ctx_accesses(struct v
int insn_cnt = env->prog->len;
struct bpf_insn insn_buf[16];
struct bpf_prog *new_prog;
- u32 cnt;
- int i;
enum bpf_access_type type;
+ int i;

if (!env->prog->aux->ops->convert_ctx_access)
return 0;

for (i = 0; i < insn_cnt; i++, insn++) {
+ u32 insn_delta, cnt;
+
if (insn->code == (BPF_LDX | BPF_MEM | BPF_W))
type = BPF_READ;
else if (insn->code == (BPF_STX | BPF_MEM | BPF_W))
@@ -2156,34 +2137,18 @@ static int convert_ctx_accesses(struct v
return -EINVAL;
}

- if (cnt == 1) {
- memcpy(insn, insn_buf, sizeof(*insn));
- continue;
- }
-
- /* several new insns need to be inserted. Make room for them */
- insn_cnt += cnt - 1;
- new_prog = bpf_prog_realloc(env->prog,
- bpf_prog_size(insn_cnt),
- GFP_USER);
+ new_prog = bpf_patch_insn_single(env->prog, i, insn_buf, cnt);
if (!new_prog)
return -ENOMEM;

- new_prog->len = insn_cnt;
-
- memmove(new_prog->insnsi + i + cnt, new_prog->insns + i + 1,
- sizeof(*insn) * (insn_cnt - i - cnt));
-
- /* copy substitute insns in place of load instruction */
- memcpy(new_prog->insnsi + i, insn_buf, sizeof(*insn) * cnt);
-
- /* adjust branches in the whole program */
- adjust_branches(new_prog, i, cnt - 1);
+ insn_delta = cnt - 1;

/* keep walking new program and skip insns we just inserted */
env->prog = new_prog;
- insn = new_prog->insnsi + i + cnt - 1;
- i += cnt - 1;
+ insn = new_prog->insnsi + i + insn_delta;
+
+ insn_cnt += insn_delta;
+ i += insn_delta;
}

return 0;

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