[PATCH bpf-next 02/11] bpf: Introduce bpf_patch

[Stanislav Fomichev <sdf@google.com>]

A simple abstraction around a series of instructions that transparently
handles resizing.

Currently, we have insn_buf[16] in convert_ctx_accesses which might
not be enough for xdp kfuncs.

If we find this abstraction helpful, we might convert existing
insn_buf[16] to it in the future.

Cc: John Fastabend <john.fastabend@gmail.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Martin KaFai Lau <martin.lau@linux.dev>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: Willem de Bruijn <willemb@google.com>
Cc: Jesper Dangaard Brouer <brouer@redhat.com>
Cc: Anatoly Burakov <anatoly.burakov@intel.com>
Cc: Alexander Lobakin <alexandr.lobakin@intel.com>
Cc: Magnus Karlsson <magnus.karlsson@gmail.com>
Cc: Maryam Tahhan <mtahhan@redhat.com>
Cc: xdp-hints@xdp-project.net
Cc: netdev@vger.kernel.org
Signed-off-by: Stanislav Fomichev <sdf@google.com>
---
 include/linux/bpf_patch.h | 29 +++++++++++++++
 kernel/bpf/Makefile       |  2 +-
 kernel/bpf/bpf_patch.c    | 77 +++++++++++++++++++++++++++++++++++++++
 3 files changed, 107 insertions(+), 1 deletion(-)
 create mode 100644 include/linux/bpf_patch.h
 create mode 100644 kernel/bpf/bpf_patch.c

diff --git a/include/linux/bpf_patch.h b/include/linux/bpf_patch.h
new file mode 100644
index 000000000000..359c165ad68b
--- /dev/null
+++ b/include/linux/bpf_patch.h
@@ -0,0 +1,29 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+#ifndef _LINUX_BPF_PATCH_H
+#define _LINUX_BPF_PATCH_H 1
+
+#include <linux/bpf.h>
+
+struct bpf_patch {
+	struct bpf_insn *insn;
+	size_t capacity;
+	size_t len;
+	int err;
+};
+
+void bpf_patch_free(struct bpf_patch *patch);
+size_t bpf_patch_len(const struct bpf_patch *patch);
+int bpf_patch_err(const struct bpf_patch *patch);
+void __bpf_patch_append(struct bpf_patch *patch, struct bpf_insn insn);
+struct bpf_insn *bpf_patch_data(const struct bpf_patch *patch);
+void bpf_patch_resolve_jmp(struct bpf_patch *patch);
+u32 bpf_patch_magles_registers(const struct bpf_patch *patch);
+
+#define bpf_patch_append(patch, ...) ({ \
+	struct bpf_insn insn[] = { __VA_ARGS__ }; \
+	int i; \
+	for (i = 0; i < ARRAY_SIZE(insn); i++) \
+		__bpf_patch_append(patch, insn[i]); \
+})
+
+#endif
diff --git a/kernel/bpf/Makefile b/kernel/bpf/Makefile
index 3a12e6b400a2..5724f36292a5 100644
--- a/kernel/bpf/Makefile
+++ b/kernel/bpf/Makefile
@@ -13,7 +13,7 @@ obj-$(CONFIG_BPF_SYSCALL) += bpf_local_storage.o bpf_task_storage.o
 obj-${CONFIG_BPF_LSM}	  += bpf_inode_storage.o
 obj-$(CONFIG_BPF_SYSCALL) += disasm.o
 obj-$(CONFIG_BPF_JIT) += trampoline.o
-obj-$(CONFIG_BPF_SYSCALL) += btf.o memalloc.o
+obj-$(CONFIG_BPF_SYSCALL) += btf.o memalloc.o bpf_patch.o
 obj-$(CONFIG_BPF_JIT) += dispatcher.o
 ifeq ($(CONFIG_NET),y)
 obj-$(CONFIG_BPF_SYSCALL) += devmap.o
diff --git a/kernel/bpf/bpf_patch.c b/kernel/bpf/bpf_patch.c
new file mode 100644
index 000000000000..eb768398fd8f
--- /dev/null
+++ b/kernel/bpf/bpf_patch.c
@@ -0,0 +1,77 @@
+// SPDX-License-Identifier: GPL-2.0-only
+
+#include <linux/bpf_patch.h>
+
+void bpf_patch_free(struct bpf_patch *patch)
+{
+	kfree(patch->insn);
+}
+
+size_t bpf_patch_len(const struct bpf_patch *patch)
+{
+	return patch->len;
+}
+
+int bpf_patch_err(const struct bpf_patch *patch)
+{
+	return patch->err;
+}
+
+void __bpf_patch_append(struct bpf_patch *patch, struct bpf_insn insn)
+{
+	void *arr;
+
+	if (patch->err)
+		return;
+
+	if (patch->len + 1 > patch->capacity) {
+		if (!patch->capacity)
+			patch->capacity = 16;
+		else
+			patch->capacity *= 2;
+
+		arr = krealloc_array(patch->insn, patch->capacity, sizeof(insn), GFP_KERNEL);
+		if (!arr) {
+			patch->err = -ENOMEM;
+			kfree(patch->insn);
+			return;
+		}
+
+		patch->insn = arr;
+		patch->capacity *= 2;
+	}
+
+	patch->insn[patch->len++] = insn;
+}
+EXPORT_SYMBOL(__bpf_patch_append);
+
+struct bpf_insn *bpf_patch_data(const struct bpf_patch *patch)
+{
+	return patch->insn;
+}
+
+void bpf_patch_resolve_jmp(struct bpf_patch *patch)
+{
+	int i;
+
+	for (i = 0; i < patch->len; i++) {
+		if (BPF_CLASS(patch->insn[i].code) != BPF_JMP)
+			continue;
+
+		if (patch->insn[i].off != S16_MAX)
+			continue;
+
+		patch->insn[i].off = patch->len - i - 1;
+	}
+}
+
+u32 bpf_patch_magles_registers(const struct bpf_patch *patch)
+{
+	u32 mask = 0;
+	int i;
+
+	for (i = 0; i < patch->len; i++)
+		mask |= 1 << patch->insn[i].dst_reg;
+
+	return mask;
+}
-- 
2.38.1.431.g37b22c650d-goog