netdev - [PATCH v2 bpf-next 5/7] x86/alternative: introduce text_poke

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Date:   Tue, 14 Dec 2021 22:01:00 -0800
From:   Song Liu <song@...nel.org>
To:     <bpf@...r.kernel.org>, <netdev@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
CC:     <ast@...nel.org>, <daniel@...earbox.net>, <andrii@...nel.org>,
        <kernel-team@...com>, <peterz@...radead.org>, <x86@...nel.org>,
        Song Liu <song@...nel.org>
Subject: [PATCH v2 bpf-next 5/7] x86/alternative: introduce text_poke_jit

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

Signed-off-by: Song Liu <song@...nel.org>
---
 arch/x86/include/asm/text-patching.h |  1 +
 arch/x86/kernel/alternative.c        | 28 ++++++++++++++++++++++++++++
 2 files changed, 29 insertions(+)

diff --git a/arch/x86/include/asm/text-patching.h b/arch/x86/include/asm/text-patching.h
index b7421780e4e9..991058c9b4b1 100644
--- a/arch/x86/include/asm/text-patching.h
+++ b/arch/x86/include/asm/text-patching.h
@@ -44,6 +44,7 @@ extern void text_poke_early(void *addr, const void *opcode, size_t len);
 extern void *text_poke(void *addr, const void *opcode, size_t len);
 extern void text_poke_sync(void);
 extern void *text_poke_kgdb(void *addr, const void *opcode, size_t len);
+extern void *text_poke_jit(void *addr, const void *opcode, size_t len);
 extern int poke_int3_handler(struct pt_regs *regs);
 extern void text_poke_bp(void *addr, const void *opcode, size_t len, const void *emulate);
 
diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index 23fb4d51a5da..02c35725cc62 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -1102,6 +1102,34 @@ void *text_poke_kgdb(void *addr, const void *opcode, size_t len)
 	return __text_poke(addr, opcode, len);
 }
 
+/**
+ * text_poke_jit - Update instructions on a live kernel by jit engine
+ * @addr: address to modify
+ * @opcode: source of the copy
+ * @len: length to copy, could be more than 2x PAGE_SIZE
+ *
+ * Only module memory taking jit text (e.g. for bpf) should be patched.
+ */
+void *text_poke_jit(void *addr, const void *opcode, size_t len)
+{
+	unsigned long start = (unsigned long)addr;
+	size_t patched = 0;
+
+	if (WARN_ON_ONCE(core_kernel_text(start)))
+		return NULL;
+
+	while (patched < len) {
+		unsigned long ptr = start + patched;
+		size_t s;
+
+		s = min_t(size_t, PAGE_SIZE * 2 - offset_in_page(ptr), len - patched);
+
+		__text_poke((void *)ptr, opcode + patched, s);
+		patched += s;
+	}
+	return addr;
+}
+
 static void do_sync_core(void *info)
 {
 	sync_core();
-- 
2.30.2