Re: [PATCH v5 6/8] powerpc: Rework and improve STRICT_KERNEL_RWX patching

Rework code-patching with STRICT_KERNEL_RWX to prepare for the next
patch which uses a temporary mm for patching under the Book3s64 Radix
MMU. Make improvements by adding a WARN_ON when the patchsite doesn't
match after patching and return the error from __patch_instruction()
properly.

Signed-off-by: Christopher M. Riedl <redacted>

---

v5:  * New to series.
---
  arch/powerpc/lib/code-patching.c | 51 +++++++++++++++++---------------
  1 file changed, 27 insertions(+), 24 deletions(-)

diff --git a/arch/powerpc/lib/code-patching.c b/arch/powerpc/lib/code-patching.c
index 3122d8e4cc013..9f2eba9b70ee4 100644
--- a/arch/powerpc/lib/code-patching.c
+++ b/arch/powerpc/lib/code-patching.c

@@ -102,11 +102,12 @@ static inline void unuse_temporary_mm(struct temp_mm *temp_mm)
  }
  
  static DEFINE_PER_CPU(struct vm_struct *, text_poke_area);
+static DEFINE_PER_CPU(unsigned long, cpu_patching_addr);
  
  #if IS_BUILTIN(CONFIG_LKDTM)
  unsigned long read_cpu_patching_addr(unsigned int cpu)
  {
-	return (unsigned long)(per_cpu(text_poke_area, cpu))->addr;
+	return per_cpu(cpu_patching_addr, cpu);
  }
  #endif
  

@@ -121,6 +122,7 @@ static int text_area_cpu_up(unsigned int cpu)
  		return -1;
  	}
  	this_cpu_write(text_poke_area, area);
+	this_cpu_write(cpu_patching_addr, (unsigned long)area->addr);
  
  	return 0;
  }

@@ -146,7 +148,7 @@ void __init poking_init(void)
  /*
   * This can be called for kernel text or a module.
   */
-static int map_patch_area(void *addr, unsigned long text_poke_addr)
+static int map_patch_area(void *addr)
  {
  	unsigned long pfn;
  	int err;

@@ -156,17 +158,20 @@ static int map_patch_area(void *addr, unsigned long text_poke_addr)
  	else
  		pfn = __pa_symbol(addr) >> PAGE_SHIFT;
  
-	err = map_kernel_page(text_poke_addr, (pfn << PAGE_SHIFT), PAGE_KERNEL);
+	err = map_kernel_page(__this_cpu_read(cpu_patching_addr),
+			      (pfn << PAGE_SHIFT), PAGE_KERNEL);
  
-	pr_devel("Mapped addr %lx with pfn %lx:%d\n", text_poke_addr, pfn, err);
+	pr_devel("Mapped addr %lx with pfn %lx:%d\n",
+		 __this_cpu_read(cpu_patching_addr), pfn, err);
  	if (err)
  		return -1;
  
  	return 0;
  }
  
-static inline int unmap_patch_area(unsigned long addr)
+static inline int unmap_patch_area(void)
  {
+	unsigned long addr = __this_cpu_read(cpu_patching_addr);
  	pte_t *ptep;
  	pmd_t *pmdp;
  	pud_t *pudp;

@@ -175,23 +180,23 @@ static inline int unmap_patch_area(unsigned long addr)
  
  	pgdp = pgd_offset_k(addr);
  	if (unlikely(!pgdp))
-		return -EINVAL;
+		goto out_err;
  
  	p4dp = p4d_offset(pgdp, addr);
  	if (unlikely(!p4dp))
-		return -EINVAL;
+		goto out_err;
  
  	pudp = pud_offset(p4dp, addr);
  	if (unlikely(!pudp))
-		return -EINVAL;
+		goto out_err;
  
  	pmdp = pmd_offset(pudp, addr);
  	if (unlikely(!pmdp))
-		return -EINVAL;
+		goto out_err;
  
  	ptep = pte_offset_kernel(pmdp, addr);
  	if (unlikely(!ptep))
-		return -EINVAL;
+		goto out_err;
  
  	pr_devel("clearing mm %p, pte %p, addr %lx\n", &init_mm, ptep, addr);
  

@@ -202,15 +207,17 @@ static inline int unmap_patch_area(unsigned long addr)
  	flush_tlb_kernel_range(addr, addr + PAGE_SIZE);
  
  	return 0;
+
+out_err:
+	pr_warn("failed to unmap %lx\n", addr);
+	return -EINVAL;

  }
  
  static int do_patch_instruction(u32 *addr, struct ppc_inst instr)
  {
-	int err;
+	int err, rc = 0;
  	u32 *patch_addr = NULL;
  	unsigned long flags;
-	unsigned long text_poke_addr;
-	unsigned long kaddr = (unsigned long)addr;
  
  	/*
  	 * During early early boot patch_instruction is called

@@ -222,24 +229,20 @@ static int do_patch_instruction(u32 *addr, struct ppc_inst instr)
  
  	local_irq_save(flags);
  
-	text_poke_addr = (unsigned long)__this_cpu_read(text_poke_area)->addr;
-	if (map_patch_area(addr, text_poke_addr)) {
-		err = -1;
+	err = map_patch_area(addr);
+	if (err)
  		goto out;
-	}
-
-	patch_addr = (u32 *)(text_poke_addr + (kaddr & ~PAGE_MASK));
  
-	__patch_instruction(addr, instr, patch_addr);
+	patch_addr = (u32 *)(__this_cpu_read(cpu_patching_addr) | offset_in_page(addr));
+	rc = __patch_instruction(addr, instr, patch_addr);
  
-	err = unmap_patch_area(text_poke_addr);
-	if (err)
-		pr_warn("failed to unmap %lx\n", text_poke_addr);
+	err = unmap_patch_area();
  
  out:
  	local_irq_restore(flags);
+	WARN_ON(!ppc_inst_equal(ppc_inst_read(addr), instr));