linux-kernel - [PATCH 1/2] tile: define a macro ktext_writable

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Date:	Wed, 30 Sep 2015 09:53:47 +0800
From:	Zhigang Lu <zlu@...hip.com>
To:	<linux-kernel@...r.kernel.org>, <cmetcalf@...hip.com>
CC:	Zhigang Lu <zlu@...hip.com>
Subject: [PATCH 1/2] tile: define a macro ktext_writable_addr to get writable kernel text address

It is used by kgdb, ftrace, kprobe and jump label, so we factor
this out into a helper routine.

Reviewed-by: Chris Metcalf <cmetcalf@...hip.com>
Signed-off-by: Zhigang Lu <zlu@...hip.com>
---
 arch/tile/include/asm/page.h | 10 ++++++++++
 arch/tile/kernel/ftrace.c    |  2 +-
 arch/tile/kernel/kgdb.c      |  2 +-
 arch/tile/kernel/kprobes.c   |  4 ++--
 4 files changed, 14 insertions(+), 4 deletions(-)

diff --git a/arch/tile/include/asm/page.h b/arch/tile/include/asm/page.h
index a213a8d..5cee2cb 100644
--- a/arch/tile/include/asm/page.h
+++ b/arch/tile/include/asm/page.h
@@ -319,6 +319,16 @@ static inline int pfn_valid(unsigned long pfn)
 #define virt_to_page(kaddr) pfn_to_page(kaddr_to_pfn((void *)(kaddr)))
 #define page_to_virt(page) pfn_to_kaddr(page_to_pfn(page))
 
+/*
+ * The kernel text is mapped at MEM_SV_START as read-only.  To allow
+ * modifying kernel text, it is also mapped at PAGE_OFFSET as read-write.
+ * This macro converts a kernel address to its writable kernel text mapping,
+ * which is used to modify the text code on a running kernel by kgdb,
+ * ftrace, kprobe, jump label, etc.
+ */
+#define ktext_writable_addr(kaddr) \
+	((unsigned long)(kaddr) - MEM_SV_START + PAGE_OFFSET)
+
 struct mm_struct;
 extern pte_t *virt_to_pte(struct mm_struct *mm, unsigned long addr);
 extern pte_t *virt_to_kpte(unsigned long kaddr);
diff --git a/arch/tile/kernel/ftrace.c b/arch/tile/kernel/ftrace.c
index 0c09961..4180ccdf 100644
--- a/arch/tile/kernel/ftrace.c
+++ b/arch/tile/kernel/ftrace.c
@@ -117,7 +117,7 @@ static int ftrace_modify_code(unsigned long pc, unsigned long old,
 		return -EINVAL;
 
 	/* Operate on writable kernel text mapping. */
-	pc_wr = pc - MEM_SV_START + PAGE_OFFSET;
+	pc_wr = ktext_writable_addr(pc);
 
 	if (probe_kernel_write((void *)pc_wr, &new, MCOUNT_INSN_SIZE))
 		return -EPERM;
diff --git a/arch/tile/kernel/kgdb.c b/arch/tile/kernel/kgdb.c
index ff5335a..a506c2c 100644
--- a/arch/tile/kernel/kgdb.c
+++ b/arch/tile/kernel/kgdb.c
@@ -164,7 +164,7 @@ static unsigned long writable_address(unsigned long addr)
 	unsigned long ret = 0;
 
 	if (core_kernel_text(addr))
-		ret = addr - MEM_SV_START + PAGE_OFFSET;
+		ret = ktext_writable_addr(addr);
 	else if (is_module_text_address(addr))
 		ret = addr;
 	else
diff --git a/arch/tile/kernel/kprobes.c b/arch/tile/kernel/kprobes.c
index f8a45c5..c68694b 100644
--- a/arch/tile/kernel/kprobes.c
+++ b/arch/tile/kernel/kprobes.c
@@ -116,7 +116,7 @@ void __kprobes arch_arm_kprobe(struct kprobe *p)
 	unsigned long addr_wr;
 
 	/* Operate on writable kernel text mapping. */
-	addr_wr = (unsigned long)p->addr - MEM_SV_START + PAGE_OFFSET;
+	addr_wr = ktext_writable_addr(p->addr);
 
 	if (probe_kernel_write((void *)addr_wr, &breakpoint_insn,
 		sizeof(breakpoint_insn)))
@@ -131,7 +131,7 @@ void __kprobes arch_disarm_kprobe(struct kprobe *kp)
 	unsigned long addr_wr;
 
 	/* Operate on writable kernel text mapping. */
-	addr_wr = (unsigned long)kp->addr - MEM_SV_START + PAGE_OFFSET;
+	addr_wr = ktext_writable_addr(kp->addr);
 
 	if (probe_kernel_write((void *)addr_wr, &kp->opcode,
 		sizeof(kp->opcode)))
-- 
2.1.2

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