[PATCH 1/2] arm: fixmap: implement __set_fixmap()

[PATCH 1/2] arm: fixmap: implement __set_fixmap()

[Rabin Vincent]

This is used from set_fixmap() and clear_fixmap() via
asm-generic/fixmap.h.

Signed-off-by: Rabin Vincent <rabin@rab.in>
---
Needs "arm: use generic fixmap.h", available in linux-next.

 arch/arm/include/asm/fixmap.h | 2 ++
 arch/arm/mm/mmu.c             | 7 +++++++
 2 files changed, 9 insertions(+)

diff --git a/arch/arm/include/asm/fixmap.h b/arch/arm/include/asm/fixmap.h
index 68ea615..55ed076 100644
--- a/arch/arm/include/asm/fixmap.h
+++ b/arch/arm/include/asm/fixmap.h
@@ -23,6 +23,8 @@ enum fixed_addresses {
 	__end_of_fixed_addresses
 };
 
+void __set_fixmap(enum fixed_addresses idx, unsigned long phys, pgprot_t prot);
+
 #include <asm-generic/fixmap.h>
 
 #endif
diff --git a/arch/arm/mm/mmu.c b/arch/arm/mm/mmu.c
index 3e16307..61bdfb1 100644
--- a/arch/arm/mm/mmu.c
+++ b/arch/arm/mm/mmu.c
@@ -22,6 +22,7 @@
 #include <asm/cputype.h>
 #include <asm/sections.h>
 #include <asm/cachetype.h>
+#include <asm/fixmap.h>
 #include <asm/sections.h>
 #include <asm/setup.h>
 #include <asm/smp_plat.h>
@@ -388,6 +389,12 @@ SET_MEMORY_FN(rw, pte_set_rw)
 SET_MEMORY_FN(x, pte_set_x)
 SET_MEMORY_FN(nx, pte_set_nx)
 
+void __set_fixmap(enum fixed_addresses idx, unsigned long phys, pgprot_t prot)
+{
+	BUG_ON(idx >= __end_of_fixed_addresses);
+	set_top_pte(__fix_to_virt(idx), pfn_pte(__phys_to_pfn(phys), prot));
+}
+
 /*
  * Adjust the PMD section entries according to the CPU in use.
  */
-- 
1.9.1

[PATCH 2/2] arm: use fixmap for text patching when text is RO

[Rabin Vincent]

Use fixmaps for text patching when the kernel text is read-only,
inspired by x86.  This makes jump labels and kprobes work with the
currently available CONFIG_DEBUG_SET_MODULE_RONX and the upcoming
CONFIG_DEBUG_RODATA options.

Signed-off-by: Rabin Vincent <rabin@rab.in>
---
 arch/arm/include/asm/fixmap.h |  3 ++
 arch/arm/kernel/jump_label.c  |  2 +-
 arch/arm/kernel/patch.c       | 66 ++++++++++++++++++++++++++++++++++++++-----
 arch/arm/kernel/patch.h       | 12 +++++++-
 4 files changed, 74 insertions(+), 9 deletions(-)

diff --git a/arch/arm/include/asm/fixmap.h b/arch/arm/include/asm/fixmap.h
index 55ed076..79c1719 100644
--- a/arch/arm/include/asm/fixmap.h
+++ b/arch/arm/include/asm/fixmap.h
@@ -18,6 +18,9 @@
 #define FIXADDR_TOP		(FIXADDR_END - PAGE_SIZE)
 
 enum fixed_addresses {
+	FIX_TEXT_POKE0,
+	FIX_TEXT_POKE1,
+
 	FIX_KMAP_BEGIN,
 	FIX_KMAP_END = (FIXADDR_TOP - FIXADDR_START) >> PAGE_SHIFT,
 	__end_of_fixed_addresses
diff --git a/arch/arm/kernel/jump_label.c b/arch/arm/kernel/jump_label.c
index 4ce4f78..afeeb9e 100644
--- a/arch/arm/kernel/jump_label.c
+++ b/arch/arm/kernel/jump_label.c
@@ -19,7 +19,7 @@ static void __arch_jump_label_transform(struct jump_entry *entry,
 		insn = arm_gen_nop();
 
 	if (is_static)
-		__patch_text(addr, insn);
+		__patch_text_early(addr, insn);
 	else
 		patch_text(addr, insn);
 }
diff --git a/arch/arm/kernel/patch.c b/arch/arm/kernel/patch.c
index 07314af..761c5b6 100644
--- a/arch/arm/kernel/patch.c
+++ b/arch/arm/kernel/patch.c
@@ -1,8 +1,11 @@
 #include <linux/kernel.h>
+#include <linux/spinlock.h>
 #include <linux/kprobes.h>
+#include <linux/mm.h>
 #include <linux/stop_machine.h>
 
 #include <asm/cacheflush.h>
+#include <asm/fixmap.h>
 #include <asm/smp_plat.h>
 #include <asm/opcodes.h>
 
@@ -13,21 +16,67 @@ struct patch {
 	unsigned int insn;
 };
 
-void __kprobes __patch_text(void *addr, unsigned int insn)
+static DEFINE_SPINLOCK(patch_lock);
+
+static void __kprobes *patch_map(void *addr, int fixmap, unsigned long *flags)
+{
+	unsigned int uintaddr = (uintptr_t) addr;
+	bool module = !core_kernel_text(uintaddr);
+	struct page *page;
+
+	if (module && IS_ENABLED(CONFIG_DEBUG_SET_MODULE_RONX)) {
+		page = vmalloc_to_page(addr);
+	} else if (!module && IS_ENABLED(CONFIG_ARM_KERNMEM_PERMS)) {
+		page = virt_to_page(addr);
+	} else {
+		return addr;
+	}
+
+	if (flags)
+		spin_lock_irqsave(&patch_lock, *flags);
+
+	set_fixmap(fixmap, page_to_phys(page));
+
+	return (void *) (__fix_to_virt(fixmap) + (uintaddr & ~PAGE_MASK));
+}
+
+static void __kprobes patch_unmap(int fixmap, unsigned long *flags)
+{
+	clear_fixmap(fixmap);
+
+	if (flags)
+		spin_unlock_irqrestore(&patch_lock, *flags);
+}
+
+void __kprobes __patch_text_real(void *addr, unsigned int insn, bool remap)
 {
 	bool thumb2 = IS_ENABLED(CONFIG_THUMB2_KERNEL);
+	unsigned int uintaddr = (uintptr_t) addr;
+	unsigned long flags;
+	void *waddr = addr;
 	int size;
 
+	if (remap)
+		waddr = patch_map(addr, FIX_TEXT_POKE0, &flags);
+
 	if (thumb2 && __opcode_is_thumb16(insn)) {
-		*(u16 *)addr = __opcode_to_mem_thumb16(insn);
+		*(u16 *)waddr = __opcode_to_mem_thumb16(insn);
 		size = sizeof(u16);
-	} else if (thumb2 && ((uintptr_t)addr & 2)) {
+	} else if (thumb2 && (uintaddr & 2)) {
+		bool twopage = (uintaddr & ~PAGE_MASK) == PAGE_SIZE - 2;
 		u16 first = __opcode_thumb32_first(insn);
 		u16 second = __opcode_thumb32_second(insn);
-		u16 *addrh = addr;
+		u16 *addrh0 = waddr;
+		u16 *addrh1 = waddr + 2;
+
+		if (remap && twopage)
+			addrh1 = patch_map(addr + 2, FIX_TEXT_POKE1, NULL);
 
-		addrh[0] = __opcode_to_mem_thumb16(first);
-		addrh[1] = __opcode_to_mem_thumb16(second);
+		*addrh0 = __opcode_to_mem_thumb16(first);
+		*addrh1 = __opcode_to_mem_thumb16(second);
+
+		if (twopage && addrh1 != addr + 2)
+			patch_unmap(FIX_TEXT_POKE1, NULL);
 
 		size = sizeof(u32);
 	} else {
@@ -36,10 +85,13 @@ void __kprobes __patch_text(void *addr, unsigned int insn)
 		else
 			insn = __opcode_to_mem_arm(insn);
 
-		*(u32 *)addr = insn;
+		*(u32 *)waddr = insn;
 		size = sizeof(u32);
 	}
 
+	if (waddr != addr)
+		patch_unmap(FIX_TEXT_POKE0, &flags);
+
 	flush_icache_range((uintptr_t)(addr),
 			   (uintptr_t)(addr) + size);
 }
diff --git a/arch/arm/kernel/patch.h b/arch/arm/kernel/patch.h
index b4731f2..77e054c 100644
--- a/arch/arm/kernel/patch.h
+++ b/arch/arm/kernel/patch.h
@@ -2,6 +2,16 @@
 #define _ARM_KERNEL_PATCH_H
 
 void patch_text(void *addr, unsigned int insn);
-void __patch_text(void *addr, unsigned int insn);
+void __patch_text_real(void *addr, unsigned int insn, bool remap);
+
+static inline void __patch_text(void *addr, unsigned int insn)
+{
+	__patch_text_real(addr, insn, true);
+}
+
+static inline void __patch_text_early(void *addr, unsigned int insn)
+{
+	__patch_text_real(addr, insn, false);
+}
 
 #endif
-- 
1.9.1

[PATCH 2/2] arm: use fixmap for text patching when text is RO

[Jon Medhurst (Tixy)]

On Fri, 2014-04-04 at 23:27 +0200, Rabin Vincent wrote:
> Use fixmaps for text patching when the kernel text is read-only,
> inspired by x86.  This makes jump labels and kprobes work with the
> currently available CONFIG_DEBUG_SET_MODULE_RONX and the upcoming
> CONFIG_DEBUG_RODATA options.
> 
> Signed-off-by: Rabin Vincent <rabin@rab.in>
> ---
>  arch/arm/include/asm/fixmap.h |  3 ++
>  arch/arm/kernel/jump_label.c  |  2 +-
>  arch/arm/kernel/patch.c       | 66 ++++++++++++++++++++++++++++++++++++++-----
>  arch/arm/kernel/patch.h       | 12 +++++++-
>  4 files changed, 74 insertions(+), 9 deletions(-)
> 
> diff --git a/arch/arm/include/asm/fixmap.h b/arch/arm/include/asm/fixmap.h
> index 55ed076..79c1719 100644
> --- a/arch/arm/include/asm/fixmap.h
> +++ b/arch/arm/include/asm/fixmap.h
> @@ -18,6 +18,9 @@
>  #define FIXADDR_TOP		(FIXADDR_END - PAGE_SIZE)
>  
>  enum fixed_addresses {
> +	FIX_TEXT_POKE0,
> +	FIX_TEXT_POKE1,
> +
>  	FIX_KMAP_BEGIN,
>  	FIX_KMAP_END = (FIXADDR_TOP - FIXADDR_START) >> PAGE_SHIFT,
>  	__end_of_fixed_addresses
> diff --git a/arch/arm/kernel/jump_label.c b/arch/arm/kernel/jump_label.c
> index 4ce4f78..afeeb9e 100644
> --- a/arch/arm/kernel/jump_label.c
> +++ b/arch/arm/kernel/jump_label.c
> @@ -19,7 +19,7 @@ static void __arch_jump_label_transform(struct jump_entry *entry,
>  		insn = arm_gen_nop();
>  
>  	if (is_static)
> -		__patch_text(addr, insn);
> +		__patch_text_early(addr, insn);
>  	else
>  		patch_text(addr, insn);
>  }
> diff --git a/arch/arm/kernel/patch.c b/arch/arm/kernel/patch.c
> index 07314af..761c5b6 100644
> --- a/arch/arm/kernel/patch.c
> +++ b/arch/arm/kernel/patch.c
> @@ -1,8 +1,11 @@
>  #include <linux/kernel.h>
> +#include <linux/spinlock.h>
>  #include <linux/kprobes.h>
> +#include <linux/mm.h>
>  #include <linux/stop_machine.h>
>  
>  #include <asm/cacheflush.h>
> +#include <asm/fixmap.h>
>  #include <asm/smp_plat.h>
>  #include <asm/opcodes.h>
>  
> @@ -13,21 +16,67 @@ struct patch {
>  	unsigned int insn;
>  };
>  
> -void __kprobes __patch_text(void *addr, unsigned int insn)
> +static DEFINE_SPINLOCK(patch_lock);
> +
> +static void __kprobes *patch_map(void *addr, int fixmap, unsigned long *flags)
> +{
> +	unsigned int uintaddr = (uintptr_t) addr;
> +	bool module = !core_kernel_text(uintaddr);
> +	struct page *page;
> +
> +	if (module && IS_ENABLED(CONFIG_DEBUG_SET_MODULE_RONX)) {
> +		page = vmalloc_to_page(addr);
> +	} else if (!module && IS_ENABLED(CONFIG_ARM_KERNMEM_PERMS)) {
> +		page = virt_to_page(addr);
> +	} else {
> +		return addr;
> +	}

I can't help but think that it'd be more maintainable to just always use
fixmap, though that would obviously have some performance impact (not
sure that particularly matters for text patching) and it would expose
possible fixmap bugginess to more kernels (see my next comment...)

> +
> +	if (flags)
> +		spin_lock_irqsave(&patch_lock, *flags);
> +
> +	set_fixmap(fixmap, page_to_phys(page));
> +
> +	return (void *) (__fix_to_virt(fixmap) + (uintaddr & ~PAGE_MASK));

How does fixmap cope with cache colouring? Looking at the implementation
it looks like it doesn't and so fixmap use on ARM is possibly buggy.

For the text patching case where we know there are no writeable mappings
[1] this should be OK if we used set_fixmap_nocache here, so long as we
also invalidated the dcache later for the proper virtual address.

[1] Can we know there are no writeable mappings though, the ftrace code
modifying patches from Kees Cook have there own way of modifying text
code permissions.

[...]

Rest of patch trimmed

-- 
Tixy

[PATCH 2/2] arm: use fixmap for text patching when text is RO

[Kees Cook]

On Mon, Apr 7, 2014 at 6:57 AM, Jon Medhurst (Tixy) <tixy@linaro.org> wrote:
> On Fri, 2014-04-04 at 23:27 +0200, Rabin Vincent wrote:
>> Use fixmaps for text patching when the kernel text is read-only,
>> inspired by x86.  This makes jump labels and kprobes work with the
>> currently available CONFIG_DEBUG_SET_MODULE_RONX and the upcoming
>> CONFIG_DEBUG_RODATA options.
>>
>> Signed-off-by: Rabin Vincent <rabin@rab.in>
>> ---
>>  arch/arm/include/asm/fixmap.h |  3 ++
>>  arch/arm/kernel/jump_label.c  |  2 +-
>>  arch/arm/kernel/patch.c       | 66 ++++++++++++++++++++++++++++++++++++++-----
>>  arch/arm/kernel/patch.h       | 12 +++++++-
>>  4 files changed, 74 insertions(+), 9 deletions(-)
>>
>> diff --git a/arch/arm/include/asm/fixmap.h b/arch/arm/include/asm/fixmap.h
>> index 55ed076..79c1719 100644
>> --- a/arch/arm/include/asm/fixmap.h
>> +++ b/arch/arm/include/asm/fixmap.h
>> @@ -18,6 +18,9 @@
>>  #define FIXADDR_TOP          (FIXADDR_END - PAGE_SIZE)
>>
>>  enum fixed_addresses {
>> +     FIX_TEXT_POKE0,
>> +     FIX_TEXT_POKE1,
>> +
>>       FIX_KMAP_BEGIN,
>>       FIX_KMAP_END = (FIXADDR_TOP - FIXADDR_START) >> PAGE_SHIFT,
>>       __end_of_fixed_addresses
>> diff --git a/arch/arm/kernel/jump_label.c b/arch/arm/kernel/jump_label.c
>> index 4ce4f78..afeeb9e 100644
>> --- a/arch/arm/kernel/jump_label.c
>> +++ b/arch/arm/kernel/jump_label.c
>> @@ -19,7 +19,7 @@ static void __arch_jump_label_transform(struct jump_entry *entry,
>>               insn = arm_gen_nop();
>>
>>       if (is_static)
>> -             __patch_text(addr, insn);
>> +             __patch_text_early(addr, insn);
>>       else
>>               patch_text(addr, insn);
>>  }
>> diff --git a/arch/arm/kernel/patch.c b/arch/arm/kernel/patch.c
>> index 07314af..761c5b6 100644
>> --- a/arch/arm/kernel/patch.c
>> +++ b/arch/arm/kernel/patch.c
>> @@ -1,8 +1,11 @@
>>  #include <linux/kernel.h>
>> +#include <linux/spinlock.h>
>>  #include <linux/kprobes.h>
>> +#include <linux/mm.h>
>>  #include <linux/stop_machine.h>
>>
>>  #include <asm/cacheflush.h>
>> +#include <asm/fixmap.h>
>>  #include <asm/smp_plat.h>
>>  #include <asm/opcodes.h>
>>
>> @@ -13,21 +16,67 @@ struct patch {
>>       unsigned int insn;
>>  };
>>
>> -void __kprobes __patch_text(void *addr, unsigned int insn)
>> +static DEFINE_SPINLOCK(patch_lock);
>> +
>> +static void __kprobes *patch_map(void *addr, int fixmap, unsigned long *flags)
>> +{
>> +     unsigned int uintaddr = (uintptr_t) addr;
>> +     bool module = !core_kernel_text(uintaddr);
>> +     struct page *page;
>> +
>> +     if (module && IS_ENABLED(CONFIG_DEBUG_SET_MODULE_RONX)) {
>> +             page = vmalloc_to_page(addr);
>> +     } else if (!module && IS_ENABLED(CONFIG_ARM_KERNMEM_PERMS)) {

I think this should probably be CONFIG_DEBUG_RODATA now that I've
moved RO exclusively into that config.

>> +             page = virt_to_page(addr);
>> +     } else {
>> +             return addr;
>> +     }
>
> I can't help but think that it'd be more maintainable to just always use
> fixmap, though that would obviously have some performance impact (not
> sure that particularly matters for text patching) and it would expose
> possible fixmap bugginess to more kernels (see my next comment...)
>
>> +
>> +     if (flags)
>> +             spin_lock_irqsave(&patch_lock, *flags);
>> +
>> +     set_fixmap(fixmap, page_to_phys(page));
>> +
>> +     return (void *) (__fix_to_virt(fixmap) + (uintaddr & ~PAGE_MASK));
>
> How does fixmap cope with cache colouring? Looking at the implementation
> it looks like it doesn't and so fixmap use on ARM is possibly buggy.
>
> For the text patching case where we know there are no writeable mappings
> [1] this should be OK if we used set_fixmap_nocache here, so long as we
> also invalidated the dcache later for the proper virtual address.
>
> [1] Can we know there are no writeable mappings though, the ftrace code
> modifying patches from Kees Cook have there own way of modifying text
> code permissions.

I think performance becomes an issue for massive updates like ftrace
seems to do, so I got the sense it was good to have the "bulk" way to
do it, and then this tiny poking way to do it.

-Kees

-- 
Kees Cook
Chrome OS Security

[PATCH 2/2] arm: use fixmap for text patching when text is RO

[Jon Medhurst (Tixy)]

On Mon, 2014-04-07 at 11:04 -0700, Kees Cook wrote:
> On Mon, Apr 7, 2014 at 6:57 AM, Jon Medhurst (Tixy) <tixy@linaro.org> wrote:
> > On Fri, 2014-04-04 at 23:27 +0200, Rabin Vincent wrote:
> >> Use fixmaps for text patching when the kernel text is read-only,
> >> inspired by x86.  This makes jump labels and kprobes work with the
> >> currently available CONFIG_DEBUG_SET_MODULE_RONX and the upcoming
> >> CONFIG_DEBUG_RODATA options.
> >>
> >> Signed-off-by: Rabin Vincent <rabin@rab.in>
> >> ---
> >>  arch/arm/include/asm/fixmap.h |  3 ++
> >>  arch/arm/kernel/jump_label.c  |  2 +-
> >>  arch/arm/kernel/patch.c       | 66 ++++++++++++++++++++++++++++++++++++++-----
> >>  arch/arm/kernel/patch.h       | 12 +++++++-
> >>  4 files changed, 74 insertions(+), 9 deletions(-)
> >>
> >> diff --git a/arch/arm/include/asm/fixmap.h b/arch/arm/include/asm/fixmap.h
> >> index 55ed076..79c1719 100644
> >> --- a/arch/arm/include/asm/fixmap.h
> >> +++ b/arch/arm/include/asm/fixmap.h
> >> @@ -18,6 +18,9 @@
> >>  #define FIXADDR_TOP          (FIXADDR_END - PAGE_SIZE)
> >>
> >>  enum fixed_addresses {
> >> +     FIX_TEXT_POKE0,
> >> +     FIX_TEXT_POKE1,
> >> +
> >>       FIX_KMAP_BEGIN,
> >>       FIX_KMAP_END = (FIXADDR_TOP - FIXADDR_START) >> PAGE_SHIFT,
> >>       __end_of_fixed_addresses
> >> diff --git a/arch/arm/kernel/jump_label.c b/arch/arm/kernel/jump_label.c
> >> index 4ce4f78..afeeb9e 100644
> >> --- a/arch/arm/kernel/jump_label.c
> >> +++ b/arch/arm/kernel/jump_label.c
> >> @@ -19,7 +19,7 @@ static void __arch_jump_label_transform(struct jump_entry *entry,
> >>               insn = arm_gen_nop();
> >>
> >>       if (is_static)
> >> -             __patch_text(addr, insn);
> >> +             __patch_text_early(addr, insn);
> >>       else
> >>               patch_text(addr, insn);
> >>  }
> >> diff --git a/arch/arm/kernel/patch.c b/arch/arm/kernel/patch.c
> >> index 07314af..761c5b6 100644
> >> --- a/arch/arm/kernel/patch.c
> >> +++ b/arch/arm/kernel/patch.c
> >> @@ -1,8 +1,11 @@
> >>  #include <linux/kernel.h>
> >> +#include <linux/spinlock.h>
> >>  #include <linux/kprobes.h>
> >> +#include <linux/mm.h>
> >>  #include <linux/stop_machine.h>
> >>
> >>  #include <asm/cacheflush.h>
> >> +#include <asm/fixmap.h>
> >>  #include <asm/smp_plat.h>
> >>  #include <asm/opcodes.h>
> >>
> >> @@ -13,21 +16,67 @@ struct patch {
> >>       unsigned int insn;
> >>  };
> >>
> >> -void __kprobes __patch_text(void *addr, unsigned int insn)
> >> +static DEFINE_SPINLOCK(patch_lock);
> >> +
> >> +static void __kprobes *patch_map(void *addr, int fixmap, unsigned long *flags)
> >> +{
> >> +     unsigned int uintaddr = (uintptr_t) addr;
> >> +     bool module = !core_kernel_text(uintaddr);
> >> +     struct page *page;
> >> +
> >> +     if (module && IS_ENABLED(CONFIG_DEBUG_SET_MODULE_RONX)) {
> >> +             page = vmalloc_to_page(addr);
> >> +     } else if (!module && IS_ENABLED(CONFIG_ARM_KERNMEM_PERMS)) {
> 
> I think this should probably be CONFIG_DEBUG_RODATA now that I've
> moved RO exclusively into that config.
> 
> >> +             page = virt_to_page(addr);
> >> +     } else {
> >> +             return addr;
> >> +     }
> >
> > I can't help but think that it'd be more maintainable to just always use
> > fixmap, though that would obviously have some performance impact (not
> > sure that particularly matters for text patching) and it would expose
> > possible fixmap bugginess to more kernels (see my next comment...)
> >
> >> +
> >> +     if (flags)
> >> +             spin_lock_irqsave(&patch_lock, *flags);
> >> +
> >> +     set_fixmap(fixmap, page_to_phys(page));
> >> +
> >> +     return (void *) (__fix_to_virt(fixmap) + (uintaddr & ~PAGE_MASK));
> >
> > How does fixmap cope with cache colouring? Looking at the implementation
> > it looks like it doesn't and so fixmap use on ARM is possibly buggy.
> >
> > For the text patching case where we know there are no writeable mappings
> > [1] this should be OK if we used set_fixmap_nocache here, so long as we
> > also invalidated the dcache later for the proper virtual address.
> >
> > [1] Can we know there are no writeable mappings though, the ftrace code
> > modifying patches from Kees Cook have there own way of modifying text
> > code permissions.
> 
> I think performance becomes an issue for massive updates like ftrace
> seems to do, so I got the sense it was good to have the "bulk" way to
> do it, and then this tiny poking way to do it.

Probably performance is significant, but as safely modifying kernel code
is virtually impossible to get right I would think that it best to
concentrate on a single method for this.

There again, the whole concept of things like ftrace is fundamentally
flawed, with it being impossible to determine all the functions which
require notrace annotations in order to avoid kernel crashes and
corruption. So perhaps a little flakiness in kprobes and ftrace is
acceptable? (I hope these things aren't enabled on distro kernels and
usable by non-root processes...)

-- 
Tixy

[PATCH 2/2] arm: use fixmap for text patching when text is RO

[Rabin Vincent]

On Mon, Apr 07, 2014 at 02:57:51PM +0100, Jon Medhurst (Tixy) wrote:
> How does fixmap cope with cache colouring? Looking at the implementation
> it looks like it doesn't and so fixmap use on ARM is possibly buggy.
> 
> For the text patching case where we know there are no writeable mappings
> [1] this should be OK if we used set_fixmap_nocache here, so long as we
> also invalidated the dcache later for the proper virtual address.

OK.  The dcache invalidation for the proper virtual address is btw
already there via the call to flush_icache_range().

> [1] Can we know there are no writeable mappings though, the ftrace code
> modifying patches from Kees Cook have there own way of modifying text
> code permissions.

The ftrace patches does the modifications and the cache cleaning in
stop_machine(), so there should not be any dirty cache lines from those
writable mappings when we set up and write to these fixmaps.  Do you
still see a problem?

[PATCH 2/2] arm: use fixmap for text patching when text is RO

[Kees Cook]

On Fri, Apr 4, 2014 at 2:27 PM, Rabin Vincent <rabin@rab.in> wrote:
> Use fixmaps for text patching when the kernel text is read-only,
> inspired by x86.  This makes jump labels and kprobes work with the
> currently available CONFIG_DEBUG_SET_MODULE_RONX and the upcoming
> CONFIG_DEBUG_RODATA options.
>
> Signed-off-by: Rabin Vincent <rabin@rab.in>
> ---
>  arch/arm/include/asm/fixmap.h |  3 ++
>  arch/arm/kernel/jump_label.c  |  2 +-
>  arch/arm/kernel/patch.c       | 66 ++++++++++++++++++++++++++++++++++++++-----
>  arch/arm/kernel/patch.h       | 12 +++++++-
>  4 files changed, 74 insertions(+), 9 deletions(-)
>
> diff --git a/arch/arm/include/asm/fixmap.h b/arch/arm/include/asm/fixmap.h
> index 55ed076..79c1719 100644
> --- a/arch/arm/include/asm/fixmap.h
> +++ b/arch/arm/include/asm/fixmap.h
> @@ -18,6 +18,9 @@
>  #define FIXADDR_TOP            (FIXADDR_END - PAGE_SIZE)
>
>  enum fixed_addresses {
> +       FIX_TEXT_POKE0,
> +       FIX_TEXT_POKE1,
> +
>         FIX_KMAP_BEGIN,
>         FIX_KMAP_END = (FIXADDR_TOP - FIXADDR_START) >> PAGE_SHIFT,
>         __end_of_fixed_addresses
> diff --git a/arch/arm/kernel/jump_label.c b/arch/arm/kernel/jump_label.c
> index 4ce4f78..afeeb9e 100644
> --- a/arch/arm/kernel/jump_label.c
> +++ b/arch/arm/kernel/jump_label.c
> @@ -19,7 +19,7 @@ static void __arch_jump_label_transform(struct jump_entry *entry,
>                 insn = arm_gen_nop();
>
>         if (is_static)
> -               __patch_text(addr, insn);
> +               __patch_text_early(addr, insn);
>         else
>                 patch_text(addr, insn);
>  }
> diff --git a/arch/arm/kernel/patch.c b/arch/arm/kernel/patch.c
> index 07314af..761c5b6 100644
> --- a/arch/arm/kernel/patch.c
> +++ b/arch/arm/kernel/patch.c
> @@ -1,8 +1,11 @@
>  #include <linux/kernel.h>
> +#include <linux/spinlock.h>
>  #include <linux/kprobes.h>
> +#include <linux/mm.h>
>  #include <linux/stop_machine.h>
>
>  #include <asm/cacheflush.h>
> +#include <asm/fixmap.h>
>  #include <asm/smp_plat.h>
>  #include <asm/opcodes.h>
>
> @@ -13,21 +16,67 @@ struct patch {
>         unsigned int insn;
>  };
>
> -void __kprobes __patch_text(void *addr, unsigned int insn)
> +static DEFINE_SPINLOCK(patch_lock);
> +
> +static void __kprobes *patch_map(void *addr, int fixmap, unsigned long *flags)
> +{
> +       unsigned int uintaddr = (uintptr_t) addr;
> +       bool module = !core_kernel_text(uintaddr);
> +       struct page *page;
> +
> +       if (module && IS_ENABLED(CONFIG_DEBUG_SET_MODULE_RONX)) {
> +               page = vmalloc_to_page(addr);
> +       } else if (!module && IS_ENABLED(CONFIG_ARM_KERNMEM_PERMS)) {
> +               page = virt_to_page(addr);
> +       } else {
> +               return addr;
> +       }
> +
> +       if (flags)
> +               spin_lock_irqsave(&patch_lock, *flags);
> +
> +       set_fixmap(fixmap, page_to_phys(page));
> +
> +       return (void *) (__fix_to_virt(fixmap) + (uintaddr & ~PAGE_MASK));
> +}
> +
> +static void __kprobes patch_unmap(int fixmap, unsigned long *flags)
> +{
> +       clear_fixmap(fixmap);
> +
> +       if (flags)
> +               spin_unlock_irqrestore(&patch_lock, *flags);
> +}
> +
> +void __kprobes __patch_text_real(void *addr, unsigned int insn, bool remap)
>  {
>         bool thumb2 = IS_ENABLED(CONFIG_THUMB2_KERNEL);
> +       unsigned int uintaddr = (uintptr_t) addr;
> +       unsigned long flags;
> +       void *waddr = addr;
>         int size;
>
> +       if (remap)
> +               waddr = patch_map(addr, FIX_TEXT_POKE0, &flags);
> +
>         if (thumb2 && __opcode_is_thumb16(insn)) {
> -               *(u16 *)addr = __opcode_to_mem_thumb16(insn);
> +               *(u16 *)waddr = __opcode_to_mem_thumb16(insn);
>                 size = sizeof(u16);
> -       } else if (thumb2 && ((uintptr_t)addr & 2)) {
> +       } else if (thumb2 && (uintaddr & 2)) {
> +               bool twopage = (uintaddr & ~PAGE_MASK) == PAGE_SIZE - 2;
>                 u16 first = __opcode_thumb32_first(insn);
>                 u16 second = __opcode_thumb32_second(insn);
> -               u16 *addrh = addr;
> +               u16 *addrh0 = waddr;
> +               u16 *addrh1 = waddr + 2;
> +
> +               if (remap && twopage)
> +                       addrh1 = patch_map(addr + 2, FIX_TEXT_POKE1, NULL);
>
> -               addrh[0] = __opcode_to_mem_thumb16(first);
> -               addrh[1] = __opcode_to_mem_thumb16(second);
> +               *addrh0 = __opcode_to_mem_thumb16(first);
> +               *addrh1 = __opcode_to_mem_thumb16(second);
> +
> +               if (twopage && addrh1 != addr + 2)
> +                       patch_unmap(FIX_TEXT_POKE1, NULL);
>
>                 size = sizeof(u32);
>         } else {
> @@ -36,10 +85,13 @@ void __kprobes __patch_text(void *addr, unsigned int insn)
>                 else
>                         insn = __opcode_to_mem_arm(insn);
>
> -               *(u32 *)addr = insn;
> +               *(u32 *)waddr = insn;
>                 size = sizeof(u32);
>         }
>
> +       if (waddr != addr)
> +               patch_unmap(FIX_TEXT_POKE0, &flags);
> +
>         flush_icache_range((uintptr_t)(addr),
>                            (uintptr_t)(addr) + size);
>  }
> diff --git a/arch/arm/kernel/patch.h b/arch/arm/kernel/patch.h
> index b4731f2..77e054c 100644
> --- a/arch/arm/kernel/patch.h
> +++ b/arch/arm/kernel/patch.h
> @@ -2,6 +2,16 @@
>  #define _ARM_KERNEL_PATCH_H
>
>  void patch_text(void *addr, unsigned int insn);
> -void __patch_text(void *addr, unsigned int insn);
> +void __patch_text_real(void *addr, unsigned int insn, bool remap);
> +
> +static inline void __patch_text(void *addr, unsigned int insn)
> +{
> +       __patch_text_real(addr, insn, true);
> +}
> +
> +static inline void __patch_text_early(void *addr, unsigned int insn)
> +{
> +       __patch_text_real(addr, insn, false);
> +}
>
>  #endif
> --
> 1.9.1
>

I think we can use this for the kgdb case too. Has anyone tried that
yet? Perhaps implementing text_poke() in terms of patch_map/unmap
calls would be best? Then the arm-specific kgdb hooks can use that,
since it does the icache flushing separately.

-Kees

-- 
Kees Cook
Chrome OS Security

[PATCH 2/2] arm: use fixmap for text patching when text is RO

[Doug Anderson]

Kees,

On Wed, Apr 23, 2014 at 2:09 PM, Kees Cook <keescook@chromium.org> wrote:

> I think we can use this for the kgdb case too. Has anyone tried that
> yet? Perhaps implementing text_poke() in terms of patch_map/unmap
> calls would be best? Then the arm-specific kgdb hooks can use that,
> since it does the icache flushing separately.

Yes.  I just tried using these patches and it worked for me.  :)  I
didn't actually implement text_poke(), though.

Atop our 3.8 tree, in case anyone is curious

* https://chromium-review.googlesource.com/196670
* https://chromium-review.googlesource.com/196671
* https://chromium-review.googlesource.com/196672
* https://chromium-review.googlesource.com/196673
* https://chromium-review.googlesource.com/196674

Please include me on the CC list for spins of your patches...

-Doug

[PATCHv2 2/2] arm: use fixmap for text patching when text is RO

[Rabin Vincent]

Use fixmaps for text patching when the kernel text is read-only,
inspired by x86.  This makes jump labels and kprobes work with the
currently available CONFIG_DEBUG_SET_MODULE_RONX and the upcoming
CONFIG_DEBUG_RODATA options.

Signed-off-by: Rabin Vincent <rabin@rab.in>
---
v2: flush the fixmap if necessary, with flush_kernel_vmap_range()

 arch/arm/include/asm/fixmap.h |  3 ++
 arch/arm/kernel/jump_label.c  |  2 +-
 arch/arm/kernel/patch.c       | 71 ++++++++++++++++++++++++++++++++++++++-----
 arch/arm/kernel/patch.h       | 12 +++++++-
 4 files changed, 79 insertions(+), 9 deletions(-)

diff --git a/arch/arm/include/asm/fixmap.h b/arch/arm/include/asm/fixmap.h
index 55ed076..79c1719 100644
--- a/arch/arm/include/asm/fixmap.h
+++ b/arch/arm/include/asm/fixmap.h
@@ -18,6 +18,9 @@
 #define FIXADDR_TOP		(FIXADDR_END - PAGE_SIZE)
 
 enum fixed_addresses {
+	FIX_TEXT_POKE0,
+	FIX_TEXT_POKE1,
+
 	FIX_KMAP_BEGIN,
 	FIX_KMAP_END = (FIXADDR_TOP - FIXADDR_START) >> PAGE_SHIFT,
 	__end_of_fixed_addresses
diff --git a/arch/arm/kernel/jump_label.c b/arch/arm/kernel/jump_label.c
index 4ce4f78..afeeb9e 100644
--- a/arch/arm/kernel/jump_label.c
+++ b/arch/arm/kernel/jump_label.c
@@ -19,7 +19,7 @@ static void __arch_jump_label_transform(struct jump_entry *entry,
 		insn = arm_gen_nop();
 
 	if (is_static)
-		__patch_text(addr, insn);
+		__patch_text_early(addr, insn);
 	else
 		patch_text(addr, insn);
 }
diff --git a/arch/arm/kernel/patch.c b/arch/arm/kernel/patch.c
index 07314af..3515b8d 100644
--- a/arch/arm/kernel/patch.c
+++ b/arch/arm/kernel/patch.c
@@ -1,8 +1,11 @@
 #include <linux/kernel.h>
+#include <linux/spinlock.h>
 #include <linux/kprobes.h>
+#include <linux/mm.h>
 #include <linux/stop_machine.h>
 
 #include <asm/cacheflush.h>
+#include <asm/fixmap.h>
 #include <asm/smp_plat.h>
 #include <asm/opcodes.h>
 
@@ -13,21 +16,70 @@ struct patch {
 	unsigned int insn;
 };
 
-void __kprobes __patch_text(void *addr, unsigned int insn)
+static DEFINE_SPINLOCK(patch_lock);
+
+static void __kprobes *patch_map(void *addr, int fixmap, unsigned long *flags)
+{
+	unsigned int uintaddr = (uintptr_t) addr;
+	bool module = !core_kernel_text(uintaddr);
+	struct page *page;
+
+	if (module && IS_ENABLED(CONFIG_DEBUG_SET_MODULE_RONX)) {
+		page = vmalloc_to_page(addr);
+	} else if (!module && IS_ENABLED(CONFIG_ARM_KERNMEM_PERMS)) {
+		page = virt_to_page(addr);
+	} else {
+		return addr;
+	}
+
+	if (flags)
+		spin_lock_irqsave(&patch_lock, *flags);
+
+	set_fixmap(fixmap, page_to_phys(page));
+
+	return (void *) (__fix_to_virt(fixmap) + (uintaddr & ~PAGE_MASK));
+}
+
+static void __kprobes patch_unmap(int fixmap, unsigned long *flags)
+{
+	clear_fixmap(fixmap);
+
+	if (flags)
+		spin_unlock_irqrestore(&patch_lock, *flags);
+}
+
+void __kprobes __patch_text_real(void *addr, unsigned int insn, bool remap)
 {
 	bool thumb2 = IS_ENABLED(CONFIG_THUMB2_KERNEL);
+	unsigned int uintaddr = (uintptr_t) addr;
+	bool twopage = false;
+	unsigned long flags;
+	void *waddr = addr;
 	int size;
 
+	if (remap)
+		waddr = patch_map(addr, FIX_TEXT_POKE0, &flags);
+
 	if (thumb2 && __opcode_is_thumb16(insn)) {
-		*(u16 *)addr = __opcode_to_mem_thumb16(insn);
+		*(u16 *)waddr = __opcode_to_mem_thumb16(insn);
 		size = sizeof(u16);
-	} else if (thumb2 && ((uintptr_t)addr & 2)) {
+	} else if (thumb2 && (uintaddr & 2)) {
 		u16 first = __opcode_thumb32_first(insn);
 		u16 second = __opcode_thumb32_second(insn);
-		u16 *addrh = addr;
+		u16 *addrh0 = waddr;
+		u16 *addrh1 = waddr + 2;
 
-		addrh[0] = __opcode_to_mem_thumb16(first);
-		addrh[1] = __opcode_to_mem_thumb16(second);
+		twopage = (uintaddr & ~PAGE_MASK) == PAGE_SIZE - 2;
+		if (twopage && remap)
+			addrh1 = patch_map(addr + 2, FIX_TEXT_POKE1, NULL);
+
+		*addrh0 = __opcode_to_mem_thumb16(first);
+		*addrh1 = __opcode_to_mem_thumb16(second);
+
+		if (twopage && addrh1 != addr + 2) {
+			flush_kernel_vmap_range(addrh1, 2);
+			patch_unmap(FIX_TEXT_POKE1, NULL);
+		}
 
 		size = sizeof(u32);
 	} else {
@@ -36,10 +88,15 @@ void __kprobes __patch_text(void *addr, unsigned int insn)
 		else
 			insn = __opcode_to_mem_arm(insn);
 
-		*(u32 *)addr = insn;
+		*(u32 *)waddr = insn;
 		size = sizeof(u32);
 	}
 
+	if (waddr != addr) {
+		flush_kernel_vmap_range(waddr, twopage ? size / 2 : size);
+		patch_unmap(FIX_TEXT_POKE0, &flags);
+	}
+
 	flush_icache_range((uintptr_t)(addr),
 			   (uintptr_t)(addr) + size);
 }
diff --git a/arch/arm/kernel/patch.h b/arch/arm/kernel/patch.h
index b4731f2..77e054c 100644
--- a/arch/arm/kernel/patch.h
+++ b/arch/arm/kernel/patch.h
@@ -2,6 +2,16 @@
 #define _ARM_KERNEL_PATCH_H
 
 void patch_text(void *addr, unsigned int insn);
-void __patch_text(void *addr, unsigned int insn);
+void __patch_text_real(void *addr, unsigned int insn, bool remap);
+
+static inline void __patch_text(void *addr, unsigned int insn)
+{
+	__patch_text_real(addr, insn, true);
+}
+
+static inline void __patch_text_early(void *addr, unsigned int insn)
+{
+	__patch_text_real(addr, insn, false);
+}
 
 #endif
-- 
1.9.2

[PATCH 1/2] arm: fixmap: implement __set_fixmap()

[Doug Anderson]

Rabin,

On Fri, Apr 4, 2014 at 2:27 PM, Rabin Vincent <rabin@rab.in> wrote:
> This is used from set_fixmap() and clear_fixmap() via
> asm-generic/fixmap.h.
>
> Signed-off-by: Rabin Vincent <rabin@rab.in>
> ---
> Needs "arm: use generic fixmap.h", available in linux-next.
>
>  arch/arm/include/asm/fixmap.h | 2 ++
>  arch/arm/mm/mmu.c             | 7 +++++++
>  2 files changed, 9 insertions(+)
>
> diff --git a/arch/arm/include/asm/fixmap.h b/arch/arm/include/asm/fixmap.h
> index 68ea615..55ed076 100644
> --- a/arch/arm/include/asm/fixmap.h
> +++ b/arch/arm/include/asm/fixmap.h
> @@ -23,6 +23,8 @@ enum fixed_addresses {
>         __end_of_fixed_addresses
>  };
>
> +void __set_fixmap(enum fixed_addresses idx, unsigned long phys, pgprot_t prot);

nit: I think you should use phys_addr_t for the physical address, right?

void __set_fixmap(enum fixed_addresses idx, phys_addr_t phys, pgprot_t prot);


...I'm no expert at fixmap, but otherwise this looks pretty reasonable to me.

-Doug