[PATCH bpf-next v3 2/3] arm64: patching: Add aarch64_insn_copy()

Puranjay Mohan
2023-06-19T10:02:13Z

This will be used by BPF JIT compiler to dump JITed binary to a RX huge
page, and thus allow multiple BPF programs sharing the a huge (2MB)
page.

The bpf_prog_pack allocator that implements the above feature allocates
a RX/RW buffer pair. The JITed code is written to the RW buffer and then
this function will be used to copy the code from RW to RX buffer.

Signed-off-by: Puranjay Mohan <puranjay12@gmail.com>
Acked-by: Song Liu <song@kernel.org>
---
Changes in v2 => v3
- No changes

Changes in v1 => v2:
- Renamed addr/opcode to dst/src.
- Added Acked-by: Song Liu <song@kernel.org>

arch/arm64/include/asm/patching.h | 1 +
arch/arm64/kernel/patching.c | 39 +++++++++++++++++++++++++++++++
2 files changed, 40 insertions(+)

diff --git a/arch/arm64/include/asm/patching.h b/arch/arm64/include/asm/patching.h
index 68908b82b168..f78a0409cbdb 100644
--- a/arch/arm64/include/asm/patching.h
+++ b/arch/arm64/include/asm/patching.h
@@ -8,6 +8,7 @@ int aarch64_insn_read(void *addr, u32 *insnp);
int aarch64_insn_write(void *addr, u32 insn);

int aarch64_insn_write_literal_u64(void *addr, u64 val);
+void *aarch64_insn_copy(void *dst, const void *src, size_t len);

int aarch64_insn_patch_text_nosync(void *addr, u32 insn);
int aarch64_insn_patch_text(void *addrs[], u32 insns[], int cnt);
diff --git a/arch/arm64/kernel/patching.c b/arch/arm64/kernel/patching.c
index b4835f6d594b..419a9428402e 100644
--- a/arch/arm64/kernel/patching.c
+++ b/arch/arm64/kernel/patching.c
@@ -105,6 +105,45 @@ noinstr int aarch64_insn_write_literal_u64(void *addr, u64 val)
return ret;
}

+/**
+ * aarch64_insn_copy - Copy instructions into (an unused part of) RX memory
+ * @dst: address to modify
+ * @src: source of the copy
+ * @len: length to copy
+ *
+ * Useful for JITs to dump new code blocks into unused regions of RX memory.
+ */
+noinstr void *aarch64_insn_copy(void *dst, const void *src, size_t len)
+{
+ unsigned long flags;
+ size_t patched = 0;
+ size_t size;
+ void *waddr;
+ void *ptr;
+ int ret;
+
+ raw_spin_lock_irqsave(&patch_lock, flags);
+
+ while (patched < len) {
+ ptr = dst + patched;
+ size = min_t(size_t, PAGE_SIZE - offset_in_page(ptr),
+ len - patched);
+
+ waddr = patch_map(ptr, FIX_TEXT_POKE0);
+ ret = copy_to_kernel_nofault(waddr, src + patched, size);
+ patch_unmap(FIX_TEXT_POKE0);
+
+ if (ret < 0) {
+ raw_spin_unlock_irqrestore(&patch_lock, flags);
+ return NULL;
+ }
+ patched += size;
+ }
+ raw_spin_unlock_irqrestore(&patch_lock, flags);
+
+ return dst;
+}
+
int __kprobes aarch64_insn_patch_text_nosync(void *addr, u32 insn)
{
u32 *tp = addr;
--
2.40.1