linux-kernel - [PATCH bpf-next 1/2] riscv: Extend patch_text

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Message-Id: <20230720154941.1504-2-puranjay12@gmail.com>
Date:   Thu, 20 Jul 2023 15:49:40 +0000
From:   Puranjay Mohan <puranjay12@...il.com>
To:     paul.walmsley@...ive.com, palmer@...belt.com,
        aou@...s.berkeley.edu, pulehui@...wei.com,
        conor.dooley@...rochip.com, ast@...nel.org, daniel@...earbox.net,
        andrii@...nel.org, martin.lau@...ux.dev, song@...nel.org,
        yhs@...com, kpsingh@...nel.org, bjorn@...nel.org,
        bpf@...r.kernel.org, linux-riscv@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Cc:     puranjay12@...il.com
Subject: [PATCH bpf-next 1/2] riscv: Extend patch_text_nosync() for multiple pages

The patch_insn_write() function currently doesn't work for multiple
pages of instructions, therefore patch_text_nosync() will fail with a
page fault if called with lengths spanning multiple pages.

This commit extends the patch_insn_write() function to support multiple
pages by copying at max 2 pages at a time in a loop. This implementation
is similar to text_poke_copy() function of x86.

Signed-off-by: Puranjay Mohan <puranjay12@...il.com>
---
 arch/riscv/kernel/patch.c | 29 ++++++++++++++++++++++++-----
 1 file changed, 24 insertions(+), 5 deletions(-)

diff --git a/arch/riscv/kernel/patch.c b/arch/riscv/kernel/patch.c
index 575e71d6c8ae..b2dbfcfdef85 100644
--- a/arch/riscv/kernel/patch.c
+++ b/arch/riscv/kernel/patch.c
@@ -53,7 +53,7 @@ static void patch_unmap(int fixmap)
 }
 NOKPROBE_SYMBOL(patch_unmap);
 
-static int patch_insn_write(void *addr, const void *insn, size_t len)
+static int __patch_insn_write(void *addr, const void *insn, size_t len)
 {
 	void *waddr = addr;
 	bool across_pages = (((uintptr_t) addr & ~PAGE_MASK) + len) > PAGE_SIZE;
@@ -74,7 +74,7 @@ static int patch_insn_write(void *addr, const void *insn, size_t len)
 		lockdep_assert_held(&text_mutex);
 
 	if (across_pages)
-		patch_map(addr + len, FIX_TEXT_POKE1);
+		patch_map(addr + PAGE_SIZE, FIX_TEXT_POKE1);
 
 	waddr = patch_map(addr, FIX_TEXT_POKE0);
 
@@ -87,15 +87,34 @@ static int patch_insn_write(void *addr, const void *insn, size_t len)
 
 	return ret;
 }
-NOKPROBE_SYMBOL(patch_insn_write);
+NOKPROBE_SYMBOL(__patch_insn_write);
 #else
-static int patch_insn_write(void *addr, const void *insn, size_t len)
+static int __patch_insn_write(void *addr, const void *insn, size_t len)
 {
 	return copy_to_kernel_nofault(addr, insn, len);
 }
-NOKPROBE_SYMBOL(patch_insn_write);
+NOKPROBE_SYMBOL(__patch_insn_write);
 #endif /* CONFIG_MMU */
 
+static int patch_insn_write(void *addr, const void *insn, size_t len)
+{
+	size_t patched = 0;
+	size_t size;
+	int ret = 0;
+
+	while (patched < len && !ret) {
+		size = min_t(size_t,
+			     PAGE_SIZE * 2 - offset_in_page(addr + patched),
+			     len - patched);
+		ret = __patch_insn_write(addr + patched, insn + patched, size);
+
+		patched += size;
+	}
+
+	return ret;
+}
+NOKPROBE_SYMBOL(patch_insn_write);
+
 int patch_text_nosync(void *addr, const void *insns, size_t len)
 {
 	u32 *tp = addr;
-- 
2.40.1