diff mbox series

[v2,3/5] powerpc/lib: Use a temporary mm for code patching

Message ID 20200709040316.12789-4-cmr@informatik.wtf (mailing list archive)
State New, archived
Headers show
Series Use per-CPU temporary mappings for patching | expand

Commit Message

Christopher M. Riedl July 9, 2020, 4:03 a.m. UTC 
Currently, code patching a STRICT_KERNEL_RWX exposes the temporary
mappings to other CPUs. These mappings should be kept local to the CPU
doing the patching. Use the pre-initialized temporary mm and patching
address for this purpose. Also add a check after patching to ensure the
patch succeeded.

Use the KUAP functions on non-BOOKS3_64 platforms since the temporary
mapping for patching uses a userspace address (to keep the mapping
local). On BOOKS3_64 platforms hash does not implement KUAP and on radix
the use of PAGE_KERNEL sets EAA[0] for the PTE which means the AMR
(KUAP) protection is ignored (see PowerISA v3.0b, Fig, 35).

Based on x86 implementation:

commit b3fd8e83ada0
("x86/alternatives: Use temporary mm for text poking")

Signed-off-by: Christopher M. Riedl <cmr@informatik.wtf>
---
 arch/powerpc/lib/code-patching.c | 152 +++++++++++--------------------
 1 file changed, 54 insertions(+), 98 deletions(-)

Comments

Christophe Leroy July 9, 2020, 7:02 a.m. UTC | #1 
Le 09/07/2020 à 06:03, Christopher M. Riedl a écrit :
> Currently, code patching a STRICT_KERNEL_RWX exposes the temporary
> mappings to other CPUs. These mappings should be kept local to the CPU
> doing the patching. Use the pre-initialized temporary mm and patching
> address for this purpose. Also add a check after patching to ensure the
> patch succeeded.

While trying the LKDTM test, I realised that this is useless for non SMP.
Is it worth applying that change to non SMP systems ?

Christophe

> 
> Use the KUAP functions on non-BOOKS3_64 platforms since the temporary
> mapping for patching uses a userspace address (to keep the mapping
> local). On BOOKS3_64 platforms hash does not implement KUAP and on radix
> the use of PAGE_KERNEL sets EAA[0] for the PTE which means the AMR
> (KUAP) protection is ignored (see PowerISA v3.0b, Fig, 35).
> 
> Based on x86 implementation:
> 
> commit b3fd8e83ada0
> ("x86/alternatives: Use temporary mm for text poking")
> 
> Signed-off-by: Christopher M. Riedl <cmr@informatik.wtf>
> ---
>   arch/powerpc/lib/code-patching.c | 152 +++++++++++--------------------
>   1 file changed, 54 insertions(+), 98 deletions(-)
> 
> diff --git a/arch/powerpc/lib/code-patching.c b/arch/powerpc/lib/code-patching.c
> index 8ae1a9e5fe6e..80fe3864f377 100644
> --- a/arch/powerpc/lib/code-patching.c
> +++ b/arch/powerpc/lib/code-patching.c
> @@ -19,6 +19,7 @@
>   #include <asm/code-patching.h>
>   #include <asm/setup.h>
>   #include <asm/inst.h>
> +#include <asm/mmu_context.h>
>   
>   static int __patch_instruction(struct ppc_inst *exec_addr, struct ppc_inst instr,
>   			       struct ppc_inst *patch_addr)
> @@ -77,106 +78,57 @@ void __init poking_init(void)
>   	pte_unmap_unlock(ptep, ptl);
>   }
>   
> -static DEFINE_PER_CPU(struct vm_struct *, text_poke_area);
> -
> -static int text_area_cpu_up(unsigned int cpu)
> -{
> -	struct vm_struct *area;
> -
> -	area = get_vm_area(PAGE_SIZE, VM_ALLOC);
> -	if (!area) {
> -		WARN_ONCE(1, "Failed to create text area for cpu %d\n",
> -			cpu);
> -		return -1;
> -	}
> -	this_cpu_write(text_poke_area, area);
> -
> -	return 0;
> -}
> -
> -static int text_area_cpu_down(unsigned int cpu)
> -{
> -	free_vm_area(this_cpu_read(text_poke_area));
> -	return 0;
> -}
> -
> -/*
> - * Run as a late init call. This allows all the boot time patching to be done
> - * simply by patching the code, and then we're called here prior to
> - * mark_rodata_ro(), which happens after all init calls are run. Although
> - * BUG_ON() is rude, in this case it should only happen if ENOMEM, and we judge
> - * it as being preferable to a kernel that will crash later when someone tries
> - * to use patch_instruction().
> - */
> -static int __init setup_text_poke_area(void)
> -{
> -	BUG_ON(!cpuhp_setup_state(CPUHP_AP_ONLINE_DYN,
> -		"powerpc/text_poke:online", text_area_cpu_up,
> -		text_area_cpu_down));
> -
> -	return 0;
> -}
> -late_initcall(setup_text_poke_area);
> +struct patch_mapping {
> +	spinlock_t *ptl; /* for protecting pte table */
> +	pte_t *ptep;
> +	struct temp_mm temp_mm;
> +};
>   
>   /*
>    * 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(const void *addr, struct patch_mapping *patch_mapping)
>   {
> -	unsigned long pfn;
> -	int err;
> +	struct page *page;
> +	pte_t pte;
> +	pgprot_t pgprot;
>   
>   	if (is_vmalloc_addr(addr))
> -		pfn = vmalloc_to_pfn(addr);
> +		page = vmalloc_to_page(addr);
>   	else
> -		pfn = __pa_symbol(addr) >> PAGE_SHIFT;
> +		page = virt_to_page(addr);
>   
> -	err = map_kernel_page(text_poke_addr, (pfn << PAGE_SHIFT), PAGE_KERNEL);
> +	if (radix_enabled())
> +		pgprot = PAGE_KERNEL;
> +	else
> +		pgprot = PAGE_SHARED;
>   
> -	pr_devel("Mapped addr %lx with pfn %lx:%d\n", text_poke_addr, pfn, err);
> -	if (err)
> +	patch_mapping->ptep = get_locked_pte(patching_mm, patching_addr,
> +					     &patch_mapping->ptl);
> +	if (unlikely(!patch_mapping->ptep)) {
> +		pr_warn("map patch: failed to allocate pte for patching\n");
>   		return -1;
> +	}
> +
> +	pte = mk_pte(page, pgprot);
> +	pte = pte_mkdirty(pte);
> +	set_pte_at(patching_mm, patching_addr, patch_mapping->ptep, pte);
> +
> +	init_temp_mm(&patch_mapping->temp_mm, patching_mm);
> +	use_temporary_mm(&patch_mapping->temp_mm);
>   
>   	return 0;
>   }
>   
> -static inline int unmap_patch_area(unsigned long addr)
> +static void unmap_patch(struct patch_mapping *patch_mapping)
>   {
> -	pte_t *ptep;
> -	pmd_t *pmdp;
> -	pud_t *pudp;
> -	p4d_t *p4dp;
> -	pgd_t *pgdp;
> -
> -	pgdp = pgd_offset_k(addr);
> -	if (unlikely(!pgdp))
> -		return -EINVAL;
> -
> -	p4dp = p4d_offset(pgdp, addr);
> -	if (unlikely(!p4dp))
> -		return -EINVAL;
> -
> -	pudp = pud_offset(p4dp, addr);
> -	if (unlikely(!pudp))
> -		return -EINVAL;
> -
> -	pmdp = pmd_offset(pudp, addr);
> -	if (unlikely(!pmdp))
> -		return -EINVAL;
> -
> -	ptep = pte_offset_kernel(pmdp, addr);
> -	if (unlikely(!ptep))
> -		return -EINVAL;
> +	/* In hash, pte_clear flushes the tlb */
> +	pte_clear(patching_mm, patching_addr, patch_mapping->ptep);
> +	unuse_temporary_mm(&patch_mapping->temp_mm);
>   
> -	pr_devel("clearing mm %p, pte %p, addr %lx\n", &init_mm, ptep, addr);
> -
> -	/*
> -	 * In hash, pte_clear flushes the tlb, in radix, we have to
> -	 */
> -	pte_clear(&init_mm, addr, ptep);
> -	flush_tlb_kernel_range(addr, addr + PAGE_SIZE);
> -
> -	return 0;
> +	/* In radix, we have to explicitly flush the tlb (no-op in hash) */
> +	local_flush_tlb_mm(patching_mm);
> +	pte_unmap_unlock(patch_mapping->ptep, patch_mapping->ptl);
>   }
>   
>   static int do_patch_instruction(struct ppc_inst *addr, struct ppc_inst instr)
> @@ -184,32 +136,36 @@ static int do_patch_instruction(struct ppc_inst *addr, struct ppc_inst instr)
>   	int err;
>   	struct ppc_inst *patch_addr = NULL;
>   	unsigned long flags;
> -	unsigned long text_poke_addr;
> -	unsigned long kaddr = (unsigned long)addr;
> +	struct patch_mapping patch_mapping;
>   
>   	/*
> -	 * 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
> +	 * The patching_mm is initialized before calling mark_rodata_ro. Prior
> +	 * to this, patch_instruction is called when we don't have (and don't
> +	 * need) the patching_mm so just do plain old patching.
>   	 */
> -	if (!this_cpu_read(text_poke_area))
> +	if (!patching_mm)
>   		return raw_patch_instruction(addr, 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(addr, &patch_mapping);
> +	if (err)
>   		goto out;
> -	}
>   
> -	patch_addr = (struct ppc_inst *)(text_poke_addr + (kaddr & ~PAGE_MASK));
> +	patch_addr = (struct ppc_inst *)(patching_addr | offset_in_page(addr));
>   
> -	__patch_instruction(addr, instr, patch_addr);
> +	if (!radix_enabled())
> +		allow_write_to_user(patch_addr, ppc_inst_len(instr));
> +	err = __patch_instruction(addr, instr, patch_addr);
> +	if (!radix_enabled())
> +		prevent_write_to_user(patch_addr, ppc_inst_len(instr));
>   
> -	err = unmap_patch_area(text_poke_addr);
> -	if (err)
> -		pr_warn("failed to unmap %lx\n", text_poke_addr);
> +	unmap_patch(&patch_mapping);
> +	/*
> +	 * Something is wrong if what we just wrote doesn't match what we
> +	 * think we just wrote.
> +	 */
> +	WARN_ON(!ppc_inst_equal(ppc_inst_read(addr), instr));
>   
>   out:
>   	local_irq_restore(flags);
>
Christopher M. Riedl July 14, 2020, 7:43 p.m. UTC | #2 
On Thu Jul 9, 2020 at 4:02 AM CDT, Christophe Leroy wrote:
>
>
> Le 09/07/2020 à 06:03, Christopher M. Riedl a écrit :
> > Currently, code patching a STRICT_KERNEL_RWX exposes the temporary
> > mappings to other CPUs. These mappings should be kept local to the CPU
> > doing the patching. Use the pre-initialized temporary mm and patching
> > address for this purpose. Also add a check after patching to ensure the
> > patch succeeded.
>
> While trying the LKDTM test, I realised that this is useless for non
> SMP.
> Is it worth applying that change to non SMP systems ?
>
> Christophe
>

Hmm, I would say it's probably preferable to maintain a single
implementation of code-patching under STRICT_KERNEL_RWX instead of
two versions for SMP and non-SMP.

> > 
> > Use the KUAP functions on non-BOOKS3_64 platforms since the temporary
> > mapping for patching uses a userspace address (to keep the mapping
> > local). On BOOKS3_64 platforms hash does not implement KUAP and on radix
> > the use of PAGE_KERNEL sets EAA[0] for the PTE which means the AMR
> > (KUAP) protection is ignored (see PowerISA v3.0b, Fig, 35).
> > 
> > Based on x86 implementation:
> > 
> > commit b3fd8e83ada0
> > ("x86/alternatives: Use temporary mm for text poking")
> > 
> > Signed-off-by: Christopher M. Riedl <cmr@informatik.wtf>
> > ---
> >   arch/powerpc/lib/code-patching.c | 152 +++++++++++--------------------
> >   1 file changed, 54 insertions(+), 98 deletions(-)
> > 
> > diff --git a/arch/powerpc/lib/code-patching.c b/arch/powerpc/lib/code-patching.c
> > index 8ae1a9e5fe6e..80fe3864f377 100644
> > --- a/arch/powerpc/lib/code-patching.c
> > +++ b/arch/powerpc/lib/code-patching.c
> > @@ -19,6 +19,7 @@
> >   #include <asm/code-patching.h>
> >   #include <asm/setup.h>
> >   #include <asm/inst.h>
> > +#include <asm/mmu_context.h>
> >   
> >   static int __patch_instruction(struct ppc_inst *exec_addr, struct ppc_inst instr,
> >   			       struct ppc_inst *patch_addr)
> > @@ -77,106 +78,57 @@ void __init poking_init(void)
> >   	pte_unmap_unlock(ptep, ptl);
> >   }
> >   
> > -static DEFINE_PER_CPU(struct vm_struct *, text_poke_area);
> > -
> > -static int text_area_cpu_up(unsigned int cpu)
> > -{
> > -	struct vm_struct *area;
> > -
> > -	area = get_vm_area(PAGE_SIZE, VM_ALLOC);
> > -	if (!area) {
> > -		WARN_ONCE(1, "Failed to create text area for cpu %d\n",
> > -			cpu);
> > -		return -1;
> > -	}
> > -	this_cpu_write(text_poke_area, area);
> > -
> > -	return 0;
> > -}
> > -
> > -static int text_area_cpu_down(unsigned int cpu)
> > -{
> > -	free_vm_area(this_cpu_read(text_poke_area));
> > -	return 0;
> > -}
> > -
> > -/*
> > - * Run as a late init call. This allows all the boot time patching to be done
> > - * simply by patching the code, and then we're called here prior to
> > - * mark_rodata_ro(), which happens after all init calls are run. Although
> > - * BUG_ON() is rude, in this case it should only happen if ENOMEM, and we judge
> > - * it as being preferable to a kernel that will crash later when someone tries
> > - * to use patch_instruction().
> > - */
> > -static int __init setup_text_poke_area(void)
> > -{
> > -	BUG_ON(!cpuhp_setup_state(CPUHP_AP_ONLINE_DYN,
> > -		"powerpc/text_poke:online", text_area_cpu_up,
> > -		text_area_cpu_down));
> > -
> > -	return 0;
> > -}
> > -late_initcall(setup_text_poke_area);
> > +struct patch_mapping {
> > +	spinlock_t *ptl; /* for protecting pte table */
> > +	pte_t *ptep;
> > +	struct temp_mm temp_mm;
> > +};
> >   
> >   /*
> >    * 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(const void *addr, struct patch_mapping *patch_mapping)
> >   {
> > -	unsigned long pfn;
> > -	int err;
> > +	struct page *page;
> > +	pte_t pte;
> > +	pgprot_t pgprot;
> >   
> >   	if (is_vmalloc_addr(addr))
> > -		pfn = vmalloc_to_pfn(addr);
> > +		page = vmalloc_to_page(addr);
> >   	else
> > -		pfn = __pa_symbol(addr) >> PAGE_SHIFT;
> > +		page = virt_to_page(addr);
> >   
> > -	err = map_kernel_page(text_poke_addr, (pfn << PAGE_SHIFT), PAGE_KERNEL);
> > +	if (radix_enabled())
> > +		pgprot = PAGE_KERNEL;
> > +	else
> > +		pgprot = PAGE_SHARED;
> >   
> > -	pr_devel("Mapped addr %lx with pfn %lx:%d\n", text_poke_addr, pfn, err);
> > -	if (err)
> > +	patch_mapping->ptep = get_locked_pte(patching_mm, patching_addr,
> > +					     &patch_mapping->ptl);
> > +	if (unlikely(!patch_mapping->ptep)) {
> > +		pr_warn("map patch: failed to allocate pte for patching\n");
> >   		return -1;
> > +	}
> > +
> > +	pte = mk_pte(page, pgprot);
> > +	pte = pte_mkdirty(pte);
> > +	set_pte_at(patching_mm, patching_addr, patch_mapping->ptep, pte);
> > +
> > +	init_temp_mm(&patch_mapping->temp_mm, patching_mm);
> > +	use_temporary_mm(&patch_mapping->temp_mm);
> >   
> >   	return 0;
> >   }
> >   
> > -static inline int unmap_patch_area(unsigned long addr)
> > +static void unmap_patch(struct patch_mapping *patch_mapping)
> >   {
> > -	pte_t *ptep;
> > -	pmd_t *pmdp;
> > -	pud_t *pudp;
> > -	p4d_t *p4dp;
> > -	pgd_t *pgdp;
> > -
> > -	pgdp = pgd_offset_k(addr);
> > -	if (unlikely(!pgdp))
> > -		return -EINVAL;
> > -
> > -	p4dp = p4d_offset(pgdp, addr);
> > -	if (unlikely(!p4dp))
> > -		return -EINVAL;
> > -
> > -	pudp = pud_offset(p4dp, addr);
> > -	if (unlikely(!pudp))
> > -		return -EINVAL;
> > -
> > -	pmdp = pmd_offset(pudp, addr);
> > -	if (unlikely(!pmdp))
> > -		return -EINVAL;
> > -
> > -	ptep = pte_offset_kernel(pmdp, addr);
> > -	if (unlikely(!ptep))
> > -		return -EINVAL;
> > +	/* In hash, pte_clear flushes the tlb */
> > +	pte_clear(patching_mm, patching_addr, patch_mapping->ptep);
> > +	unuse_temporary_mm(&patch_mapping->temp_mm);
> >   
> > -	pr_devel("clearing mm %p, pte %p, addr %lx\n", &init_mm, ptep, addr);
> > -
> > -	/*
> > -	 * In hash, pte_clear flushes the tlb, in radix, we have to
> > -	 */
> > -	pte_clear(&init_mm, addr, ptep);
> > -	flush_tlb_kernel_range(addr, addr + PAGE_SIZE);
> > -
> > -	return 0;
> > +	/* In radix, we have to explicitly flush the tlb (no-op in hash) */
> > +	local_flush_tlb_mm(patching_mm);
> > +	pte_unmap_unlock(patch_mapping->ptep, patch_mapping->ptl);
> >   }
> >   
> >   static int do_patch_instruction(struct ppc_inst *addr, struct ppc_inst instr)
> > @@ -184,32 +136,36 @@ static int do_patch_instruction(struct ppc_inst *addr, struct ppc_inst instr)
> >   	int err;
> >   	struct ppc_inst *patch_addr = NULL;
> >   	unsigned long flags;
> > -	unsigned long text_poke_addr;
> > -	unsigned long kaddr = (unsigned long)addr;
> > +	struct patch_mapping patch_mapping;
> >   
> >   	/*
> > -	 * 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
> > +	 * The patching_mm is initialized before calling mark_rodata_ro. Prior
> > +	 * to this, patch_instruction is called when we don't have (and don't
> > +	 * need) the patching_mm so just do plain old patching.
> >   	 */
> > -	if (!this_cpu_read(text_poke_area))
> > +	if (!patching_mm)
> >   		return raw_patch_instruction(addr, 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(addr, &patch_mapping);
> > +	if (err)
> >   		goto out;
> > -	}
> >   
> > -	patch_addr = (struct ppc_inst *)(text_poke_addr + (kaddr & ~PAGE_MASK));
> > +	patch_addr = (struct ppc_inst *)(patching_addr | offset_in_page(addr));
> >   
> > -	__patch_instruction(addr, instr, patch_addr);
> > +	if (!radix_enabled())
> > +		allow_write_to_user(patch_addr, ppc_inst_len(instr));
> > +	err = __patch_instruction(addr, instr, patch_addr);
> > +	if (!radix_enabled())
> > +		prevent_write_to_user(patch_addr, ppc_inst_len(instr));
> >   
> > -	err = unmap_patch_area(text_poke_addr);
> > -	if (err)
> > -		pr_warn("failed to unmap %lx\n", text_poke_addr);
> > +	unmap_patch(&patch_mapping);
> > +	/*
> > +	 * Something is wrong if what we just wrote doesn't match what we
> > +	 * think we just wrote.
> > +	 */
> > +	WARN_ON(!ppc_inst_equal(ppc_inst_read(addr), instr));
> >   
> >   out:
> >   	local_irq_restore(flags);
> >
diff mbox series

Patch

diff --git a/arch/powerpc/lib/code-patching.c b/arch/powerpc/lib/code-patching.c
index 8ae1a9e5fe6e..80fe3864f377 100644
--- a/arch/powerpc/lib/code-patching.c
+++ b/arch/powerpc/lib/code-patching.c
@@ -19,6 +19,7 @@ 
 #include <asm/code-patching.h>
 #include <asm/setup.h>
 #include <asm/inst.h>
+#include <asm/mmu_context.h>
 
 static int __patch_instruction(struct ppc_inst *exec_addr, struct ppc_inst instr,
 			       struct ppc_inst *patch_addr)
@@ -77,106 +78,57 @@  void __init poking_init(void)
 	pte_unmap_unlock(ptep, ptl);
 }
 
-static DEFINE_PER_CPU(struct vm_struct *, text_poke_area);
-
-static int text_area_cpu_up(unsigned int cpu)
-{
-	struct vm_struct *area;
-
-	area = get_vm_area(PAGE_SIZE, VM_ALLOC);
-	if (!area) {
-		WARN_ONCE(1, "Failed to create text area for cpu %d\n",
-			cpu);
-		return -1;
-	}
-	this_cpu_write(text_poke_area, area);
-
-	return 0;
-}
-
-static int text_area_cpu_down(unsigned int cpu)
-{
-	free_vm_area(this_cpu_read(text_poke_area));
-	return 0;
-}
-
-/*
- * Run as a late init call. This allows all the boot time patching to be done
- * simply by patching the code, and then we're called here prior to
- * mark_rodata_ro(), which happens after all init calls are run. Although
- * BUG_ON() is rude, in this case it should only happen if ENOMEM, and we judge
- * it as being preferable to a kernel that will crash later when someone tries
- * to use patch_instruction().
- */
-static int __init setup_text_poke_area(void)
-{
-	BUG_ON(!cpuhp_setup_state(CPUHP_AP_ONLINE_DYN,
-		"powerpc/text_poke:online", text_area_cpu_up,
-		text_area_cpu_down));
-
-	return 0;
-}
-late_initcall(setup_text_poke_area);
+struct patch_mapping {
+	spinlock_t *ptl; /* for protecting pte table */
+	pte_t *ptep;
+	struct temp_mm temp_mm;
+};
 
 /*
  * 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(const void *addr, struct patch_mapping *patch_mapping)
 {
-	unsigned long pfn;
-	int err;
+	struct page *page;
+	pte_t pte;
+	pgprot_t pgprot;
 
 	if (is_vmalloc_addr(addr))
-		pfn = vmalloc_to_pfn(addr);
+		page = vmalloc_to_page(addr);
 	else
-		pfn = __pa_symbol(addr) >> PAGE_SHIFT;
+		page = virt_to_page(addr);
 
-	err = map_kernel_page(text_poke_addr, (pfn << PAGE_SHIFT), PAGE_KERNEL);
+	if (radix_enabled())
+		pgprot = PAGE_KERNEL;
+	else
+		pgprot = PAGE_SHARED;
 
-	pr_devel("Mapped addr %lx with pfn %lx:%d\n", text_poke_addr, pfn, err);
-	if (err)
+	patch_mapping->ptep = get_locked_pte(patching_mm, patching_addr,
+					     &patch_mapping->ptl);
+	if (unlikely(!patch_mapping->ptep)) {
+		pr_warn("map patch: failed to allocate pte for patching\n");
 		return -1;
+	}
+
+	pte = mk_pte(page, pgprot);
+	pte = pte_mkdirty(pte);
+	set_pte_at(patching_mm, patching_addr, patch_mapping->ptep, pte);
+
+	init_temp_mm(&patch_mapping->temp_mm, patching_mm);
+	use_temporary_mm(&patch_mapping->temp_mm);
 
 	return 0;
 }
 
-static inline int unmap_patch_area(unsigned long addr)
+static void unmap_patch(struct patch_mapping *patch_mapping)
 {
-	pte_t *ptep;
-	pmd_t *pmdp;
-	pud_t *pudp;
-	p4d_t *p4dp;
-	pgd_t *pgdp;
-
-	pgdp = pgd_offset_k(addr);
-	if (unlikely(!pgdp))
-		return -EINVAL;
-
-	p4dp = p4d_offset(pgdp, addr);
-	if (unlikely(!p4dp))
-		return -EINVAL;
-
-	pudp = pud_offset(p4dp, addr);
-	if (unlikely(!pudp))
-		return -EINVAL;
-
-	pmdp = pmd_offset(pudp, addr);
-	if (unlikely(!pmdp))
-		return -EINVAL;
-
-	ptep = pte_offset_kernel(pmdp, addr);
-	if (unlikely(!ptep))
-		return -EINVAL;
+	/* In hash, pte_clear flushes the tlb */
+	pte_clear(patching_mm, patching_addr, patch_mapping->ptep);
+	unuse_temporary_mm(&patch_mapping->temp_mm);
 
-	pr_devel("clearing mm %p, pte %p, addr %lx\n", &init_mm, ptep, addr);
-
-	/*
-	 * In hash, pte_clear flushes the tlb, in radix, we have to
-	 */
-	pte_clear(&init_mm, addr, ptep);
-	flush_tlb_kernel_range(addr, addr + PAGE_SIZE);
-
-	return 0;
+	/* In radix, we have to explicitly flush the tlb (no-op in hash) */
+	local_flush_tlb_mm(patching_mm);
+	pte_unmap_unlock(patch_mapping->ptep, patch_mapping->ptl);
 }
 
 static int do_patch_instruction(struct ppc_inst *addr, struct ppc_inst instr)
@@ -184,32 +136,36 @@  static int do_patch_instruction(struct ppc_inst *addr, struct ppc_inst instr)
 	int err;
 	struct ppc_inst *patch_addr = NULL;
 	unsigned long flags;
-	unsigned long text_poke_addr;
-	unsigned long kaddr = (unsigned long)addr;
+	struct patch_mapping patch_mapping;
 
 	/*
-	 * 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
+	 * The patching_mm is initialized before calling mark_rodata_ro. Prior
+	 * to this, patch_instruction is called when we don't have (and don't
+	 * need) the patching_mm so just do plain old patching.
 	 */
-	if (!this_cpu_read(text_poke_area))
+	if (!patching_mm)
 		return raw_patch_instruction(addr, 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(addr, &patch_mapping);
+	if (err)
 		goto out;
-	}
 
-	patch_addr = (struct ppc_inst *)(text_poke_addr + (kaddr & ~PAGE_MASK));
+	patch_addr = (struct ppc_inst *)(patching_addr | offset_in_page(addr));
 
-	__patch_instruction(addr, instr, patch_addr);
+	if (!radix_enabled())
+		allow_write_to_user(patch_addr, ppc_inst_len(instr));
+	err = __patch_instruction(addr, instr, patch_addr);
+	if (!radix_enabled())
+		prevent_write_to_user(patch_addr, ppc_inst_len(instr));
 
-	err = unmap_patch_area(text_poke_addr);
-	if (err)
-		pr_warn("failed to unmap %lx\n", text_poke_addr);
+	unmap_patch(&patch_mapping);
+	/*
+	 * Something is wrong if what we just wrote doesn't match what we
+	 * think we just wrote.
+	 */
+	WARN_ON(!ppc_inst_equal(ppc_inst_read(addr), instr));
 
 out:
 	local_irq_restore(flags);