[PATCH 1/6] powerpc/code-patching: Implement generic text patching function

[Benjamin Gray <bgray@linux.ibm.com>]

Adds a generic text patching mechanism for patches of 1, 2, 4, or 8
bytes. The patcher conditionally syncs the icache depending on if
the content will be executed (as opposed to, e.g., read-only data).

The `patch_instruction` function is reimplemented in terms of this
more generic function. This generic implementation allows patching of
arbitrary 64-bit data, whereas the original `patch_instruction` decided
the size based on the 'instruction' opcode, so was not suitable for
arbitrary data.

Signed-off-by: Benjamin Gray <bgray@linux.ibm.com>
---
 arch/powerpc/include/asm/code-patching.h |   1 +
 arch/powerpc/lib/code-patching.c         | 135 +++++++++++++++--------
 2 files changed, 89 insertions(+), 47 deletions(-)

diff --git a/arch/powerpc/include/asm/code-patching.h b/arch/powerpc/include/asm/code-patching.h
index 1c6316ec4b74..6a52c19dae46 100644
--- a/arch/powerpc/include/asm/code-patching.h
+++ b/arch/powerpc/include/asm/code-patching.h
@@ -76,6 +76,7 @@ int create_cond_branch(ppc_inst_t *instr, const u32 *addr,
 int patch_branch(u32 *addr, unsigned long target, int flags);
 int patch_instruction(u32 *addr, ppc_inst_t instr);
 int raw_patch_instruction(u32 *addr, ppc_inst_t instr);
+int patch_text_data(void *dest, const void *src, size_t size);
 
 static inline unsigned long patch_site_addr(s32 *site)
 {
diff --git a/arch/powerpc/lib/code-patching.c b/arch/powerpc/lib/code-patching.c
index ad0cf3108dd0..a09a0898c2ce 100644
--- a/arch/powerpc/lib/code-patching.c
+++ b/arch/powerpc/lib/code-patching.c
@@ -3,6 +3,7 @@
  *  Copyright 2008 Michael Ellerman, IBM Corporation.
  */
 
+#include <linux/mm.h>
 #include <linux/kprobes.h>
 #include <linux/vmalloc.h>
 #include <linux/init.h>
@@ -14,32 +15,7 @@
 #include <asm/page.h>
 #include <asm/code-patching.h>
 #include <asm/inst.h>
-
-static int __patch_instruction(u32 *exec_addr, ppc_inst_t instr, u32 *patch_addr)
-{
-	if (!ppc_inst_prefixed(instr)) {
-		u32 val = ppc_inst_val(instr);
-
-		__put_kernel_nofault(patch_addr, &val, u32, failed);
-	} else {
-		u64 val = ppc_inst_as_ulong(instr);
-
-		__put_kernel_nofault(patch_addr, &val, u64, failed);
-	}
-
-	asm ("dcbst 0, %0; sync; icbi 0,%1; sync; isync" :: "r" (patch_addr),
-							    "r" (exec_addr));
-
-	return 0;
-
-failed:
-	return -EPERM;
-}
-
-int raw_patch_instruction(u32 *addr, ppc_inst_t instr)
-{
-	return __patch_instruction(addr, instr, addr);
-}
+#include <asm/cacheflush.h>
 
 #ifdef CONFIG_STRICT_KERNEL_RWX
 static DEFINE_PER_CPU(struct vm_struct *, text_poke_area);
@@ -147,16 +123,44 @@ static void unmap_patch_area(unsigned long addr)
 	flush_tlb_kernel_range(addr, addr + PAGE_SIZE);
 }
 
-static int __do_patch_instruction(u32 *addr, ppc_inst_t instr)
+static int __patch_text(void *dest, const void *src, size_t size, bool is_exec, void *exec_addr)
+{
+	if (virt_to_pfn(dest) != virt_to_pfn(dest + size - 1))
+		return -EFAULT;
+
+	switch (size) {
+		case 1:
+			__put_kernel_nofault(dest, src, u8, failed);
+			break;
+		case 2:
+			__put_kernel_nofault(dest, src, u16, failed);
+			break;
+		case 4:
+			__put_kernel_nofault(dest, src, u32, failed);
+			break;
+		case 8:
+			__put_kernel_nofault(dest, src, u64, failed);
+			break;
+	}
+
+	asm ("dcbst 0, %0; sync" :: "r" (dest));
+
+	if (is_exec)
+		asm ("icbi 0,%0; sync; isync" :: "r" (exec_addr));
+
+	return 0;
+
+failed:
+	return -EPERM;
+}
+
+static pte_t *start_text_patch(void* dest, u32 **patch_addr)
 {
-	int err;
-	u32 *patch_addr;
-	unsigned long text_poke_addr;
 	pte_t *pte;
-	unsigned long pfn = get_patch_pfn(addr);
+	unsigned long text_poke_addr = (unsigned long)__this_cpu_read(text_poke_area)->addr & PAGE_MASK;
+	unsigned long pfn = get_patch_pfn(dest);
 
-	text_poke_addr = (unsigned long)__this_cpu_read(text_poke_area)->addr & PAGE_MASK;
-	patch_addr = (u32 *)(text_poke_addr + offset_in_page(addr));
+	*patch_addr = (u32 *)(text_poke_addr + offset_in_page(dest));
 
 	pte = virt_to_kpte(text_poke_addr);
 	__set_pte_at(&init_mm, text_poke_addr, pte, pfn_pte(pfn, PAGE_KERNEL), 0);
@@ -164,33 +168,63 @@ static int __do_patch_instruction(u32 *addr, ppc_inst_t instr)
 	if (radix_enabled())
 		asm volatile("ptesync": : :"memory");
 
-	err = __patch_instruction(addr, instr, patch_addr);
+	return pte;
+}
 
+static void finish_text_patch(pte_t *pte)
+{
+	unsigned long text_poke_addr = (unsigned long)__this_cpu_read(text_poke_area)->addr & PAGE_MASK;
 	pte_clear(&init_mm, text_poke_addr, pte);
 	flush_tlb_kernel_range(text_poke_addr, text_poke_addr + PAGE_SIZE);
+}
+
+static int do_patch_text(void *dest, const void *src, size_t size, bool is_exec)
+{
+	int err;
+	pte_t *pte;
+	u32 *patch_addr;
+
+	pte = start_text_patch(dest, &patch_addr);
+	err = __patch_text(patch_addr, src, size, is_exec, dest);
+	finish_text_patch(pte);
 
 	return err;
 }
 
-static int do_patch_instruction(u32 *addr, ppc_inst_t instr)
+static int patch_text(void *dest, const void *src, size_t size, bool is_exec)
 {
 	int err;
 	unsigned long flags;
 
-	/*
-	 * During early early boot patch_instruction is called
-	 * when text_poke_area is not ready, but we still need
-	 * to allow patching. We just do the plain old patching
-	 */
+	/* Make sure we aren't patching a freed init section */
+	if (static_branch_likely(&init_mem_is_free) && init_section_contains(dest, 4))
+		return 0;
+
 	if (!static_branch_likely(&poking_init_done))
-		return raw_patch_instruction(addr, instr);
+		return __patch_text(dest, src, size, is_exec, dest);
 
 	local_irq_save(flags);
-	err = __do_patch_instruction(addr, instr);
+	err = do_patch_text(dest, src, size, is_exec);
 	local_irq_restore(flags);
 
 	return err;
 }
+
+int patch_text_data(void *dest, const void *src, size_t size) {
+	return patch_text(dest, src, size, false);
+}
+
+int raw_patch_instruction(u32 *addr, ppc_inst_t instr)
+{
+	if (!ppc_inst_prefixed(instr)) {
+		u32 val = ppc_inst_val(instr);
+		return __patch_text(addr, &val, sizeof(val), true, addr);
+	} else {
+		u64 val = ppc_inst_as_ulong(instr);
+		return __patch_text(addr, &val, sizeof(val), true, addr);
+	}
+}
+
 #else /* !CONFIG_STRICT_KERNEL_RWX */
 
 static int do_patch_instruction(u32 *addr, ppc_inst_t instr)
@@ -198,17 +232,24 @@ static int do_patch_instruction(u32 *addr, ppc_inst_t instr)
 	return raw_patch_instruction(addr, instr);
 }
 
+void *patch_memory(void *dest, const void *src, size_t size)
+{
+	return memcpy(dest, src, size);
+}
+
 #endif /* CONFIG_STRICT_KERNEL_RWX */
 
 __ro_after_init DEFINE_STATIC_KEY_FALSE(init_mem_is_free);
 
 int patch_instruction(u32 *addr, ppc_inst_t instr)
 {
-	/* Make sure we aren't patching a freed init section */
-	if (static_branch_likely(&init_mem_is_free) && init_section_contains(addr, 4))
-		return 0;
-
-	return do_patch_instruction(addr, instr);
+	if (!ppc_inst_prefixed(instr)) {
+		u32 val = ppc_inst_val(instr);
+		return patch_text(addr, &val, sizeof(val), true);
+	} else {
+		u64 val = ppc_inst_as_ulong(instr);
+		return patch_text(addr, &val, sizeof(val), true);
+	}
 }
 NOKPROBE_SYMBOL(patch_instruction);
 
-- 
2.37.3