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From:   Puranjay Mohan <puranjay12@gmail.com>
To:     ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org,
        martin.lau@linux.dev, song@kernel.org, catalin.marinas@arm.com,
        mark.rutland@arm.com, bpf@vger.kernel.org, kpsingh@kernel.org,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org
Cc:     puranjay12@gmail.com
Subject: [PATCH bpf-next 2/3] arm64: patching: Add aarch64_insn_copy()
Date:   Mon,  5 Jun 2023 07:40:23 +0000
Message-Id: <20230605074024.1055863-3-puranjay12@gmail.com>
In-Reply-To: <20230605074024.1055863-1-puranjay12@gmail.com>
References: <20230605074024.1055863-1-puranjay12@gmail.com>
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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>
---
 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..dba9eb392bf1 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 *addr, const void *opcode, 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..48c710f6a1ff 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
+ * @addr: address to modify
+ * @opcode: 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 *addr, const void *opcode, size_t len)
+{
+	unsigned long flags;
+	size_t patched = 0;
+	size_t size;
+	void *waddr;
+	void *dst;
+	int ret;
+
+	raw_spin_lock_irqsave(&patch_lock, flags);
+
+	while (patched < len) {
+		dst = addr + patched;
+		size = min_t(size_t, PAGE_SIZE - offset_in_page(dst),
+			     len - patched);
+
+		waddr = patch_map(dst, FIX_TEXT_POKE0);
+		ret = copy_to_kernel_nofault(waddr, opcode + 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 addr;
+}
+
 int __kprobes aarch64_insn_patch_text_nosync(void *addr, u32 insn)
 {
 	u32 *tp = addr;
-- 
2.39.2