arm64: kprobes: call set_memory_rox() for kprobe page

[v2 PATCH] arm64: kprobes: call set_memory_rox() for kprobe page

Posted by Yang Shi 1 week, 6 days ago

The kprobe page is allocated by execmem allocator with ROX permission.
It needs to call set_memory_rox() to set proper permission for the
direct map too. It was missed.

Fixes: 10d5e97c1bf8 ("arm64: use PAGE_KERNEL_ROX directly in alloc_insn_page")
Cc: <stable@vger.kernel.org>
Signed-off-by: Yang Shi <yang@os.amperecomputing.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
---
v2: Separated the patch from BBML2 series since it is an orthogonal bug
    fix per Ryan.
    Fixed the variable name nit per Catalin.
    Collected R-bs from Catalin.

 arch/arm64/kernel/probes/kprobes.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/arch/arm64/kernel/probes/kprobes.c b/arch/arm64/kernel/probes/kprobes.c
index 0c5d408afd95..8ab6104a4883 100644
--- a/arch/arm64/kernel/probes/kprobes.c
+++ b/arch/arm64/kernel/probes/kprobes.c
@@ -10,6 +10,7 @@
 
 #define pr_fmt(fmt) "kprobes: " fmt
 
+#include <linux/execmem.h>
 #include <linux/extable.h>
 #include <linux/kasan.h>
 #include <linux/kernel.h>
@@ -41,6 +42,17 @@ DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);
 static void __kprobes
 post_kprobe_handler(struct kprobe *, struct kprobe_ctlblk *, struct pt_regs *);
 
+void *alloc_insn_page(void)
+{
+	void *addr;
+
+	addr = execmem_alloc(EXECMEM_KPROBES, PAGE_SIZE);
+	if (!addr)
+		return NULL;
+	set_memory_rox((unsigned long)addr, 1);
+	return addr;
+}
+
 static void __kprobes arch_prepare_ss_slot(struct kprobe *p)
 {
 	kprobe_opcode_t *addr = p->ainsn.xol_insn;
-- 
2.47.0

Re: [v2 PATCH] arm64: kprobes: call set_memory_rox() for kprobe page

Posted by Will Deacon 1 week, 6 days ago

On Thu, Sep 18, 2025 at 09:23:49AM -0700, Yang Shi wrote:
> The kprobe page is allocated by execmem allocator with ROX permission.
> It needs to call set_memory_rox() to set proper permission for the
> direct map too. It was missed.
> 
> Fixes: 10d5e97c1bf8 ("arm64: use PAGE_KERNEL_ROX directly in alloc_insn_page")
> Cc: <stable@vger.kernel.org>
> Signed-off-by: Yang Shi <yang@os.amperecomputing.com>
> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
> ---
> v2: Separated the patch from BBML2 series since it is an orthogonal bug
>     fix per Ryan.
>     Fixed the variable name nit per Catalin.
>     Collected R-bs from Catalin.
> 
>  arch/arm64/kernel/probes/kprobes.c | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> diff --git a/arch/arm64/kernel/probes/kprobes.c b/arch/arm64/kernel/probes/kprobes.c
> index 0c5d408afd95..8ab6104a4883 100644
> --- a/arch/arm64/kernel/probes/kprobes.c
> +++ b/arch/arm64/kernel/probes/kprobes.c
> @@ -10,6 +10,7 @@
>  
>  #define pr_fmt(fmt) "kprobes: " fmt
>  
> +#include <linux/execmem.h>
>  #include <linux/extable.h>
>  #include <linux/kasan.h>
>  #include <linux/kernel.h>
> @@ -41,6 +42,17 @@ DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);
>  static void __kprobes
>  post_kprobe_handler(struct kprobe *, struct kprobe_ctlblk *, struct pt_regs *);
>  
> +void *alloc_insn_page(void)
> +{
> +	void *addr;
> +
> +	addr = execmem_alloc(EXECMEM_KPROBES, PAGE_SIZE);
> +	if (!addr)
> +		return NULL;
> +	set_memory_rox((unsigned long)addr, 1);
> +	return addr;
> +}

Why isn't execmem taking care of this? It looks to me like the
execmem_cache_alloc() path calls set_memory_rox() but the
execmem_vmalloc() path doesn't?

It feels a bit bizarre to me that we have to provide our own wrapper
(which is identical to what s390 does). Also, how does alloc_insn_page()
handle the direct map alias on x86?

Will

Re: [v2 PATCH] arm64: kprobes: call set_memory_rox() for kprobe page

Posted by Dev Jain 1 week, 6 days ago

On 18/09/25 10:56 pm, Will Deacon wrote:
> On Thu, Sep 18, 2025 at 09:23:49AM -0700, Yang Shi wrote:
>> The kprobe page is allocated by execmem allocator with ROX permission.
>> It needs to call set_memory_rox() to set proper permission for the
>> direct map too. It was missed.
>>
>> Fixes: 10d5e97c1bf8 ("arm64: use PAGE_KERNEL_ROX directly in alloc_insn_page")
>> Cc: <stable@vger.kernel.org>
>> Signed-off-by: Yang Shi <yang@os.amperecomputing.com>
>> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
>> ---
>> v2: Separated the patch from BBML2 series since it is an orthogonal bug
>>      fix per Ryan.
>>      Fixed the variable name nit per Catalin.
>>      Collected R-bs from Catalin.
>>
>>   arch/arm64/kernel/probes/kprobes.c | 12 ++++++++++++
>>   1 file changed, 12 insertions(+)
>>
>> diff --git a/arch/arm64/kernel/probes/kprobes.c b/arch/arm64/kernel/probes/kprobes.c
>> index 0c5d408afd95..8ab6104a4883 100644
>> --- a/arch/arm64/kernel/probes/kprobes.c
>> +++ b/arch/arm64/kernel/probes/kprobes.c
>> @@ -10,6 +10,7 @@
>>   
>>   #define pr_fmt(fmt) "kprobes: " fmt
>>   
>> +#include <linux/execmem.h>
>>   #include <linux/extable.h>
>>   #include <linux/kasan.h>
>>   #include <linux/kernel.h>
>> @@ -41,6 +42,17 @@ DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);
>>   static void __kprobes
>>   post_kprobe_handler(struct kprobe *, struct kprobe_ctlblk *, struct pt_regs *);
>>   
>> +void *alloc_insn_page(void)
>> +{
>> +	void *addr;
>> +
>> +	addr = execmem_alloc(EXECMEM_KPROBES, PAGE_SIZE);
>> +	if (!addr)
>> +		return NULL;
>> +	set_memory_rox((unsigned long)addr, 1);
>> +	return addr;
>> +}
> Why isn't execmem taking care of this? It looks to me like the
> execmem_cache_alloc() path calls set_memory_rox() but the
> execmem_vmalloc() path doesn't?

Ryan has raised this issue here -
https://lore.kernel.org/all/d4019be7-e24c-4715-a42a-4f1fc39a9bd4@arm.com/

>
> It feels a bit bizarre to me that we have to provide our own wrapper
> (which is identical to what s390 does). Also, how does alloc_insn_page()
> handle the direct map alias on x86?
>
> Will
>

Re: [v2 PATCH] arm64: kprobes: call set_memory_rox() for kprobe page

Posted by Yang Shi 1 week, 6 days ago


On 9/18/25 10:26 AM, Will Deacon wrote:
> On Thu, Sep 18, 2025 at 09:23:49AM -0700, Yang Shi wrote:
>> The kprobe page is allocated by execmem allocator with ROX permission.
>> It needs to call set_memory_rox() to set proper permission for the
>> direct map too. It was missed.
>>
>> Fixes: 10d5e97c1bf8 ("arm64: use PAGE_KERNEL_ROX directly in alloc_insn_page")
>> Cc: <stable@vger.kernel.org>
>> Signed-off-by: Yang Shi <yang@os.amperecomputing.com>
>> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
>> ---
>> v2: Separated the patch from BBML2 series since it is an orthogonal bug
>>      fix per Ryan.
>>      Fixed the variable name nit per Catalin.
>>      Collected R-bs from Catalin.
>>
>>   arch/arm64/kernel/probes/kprobes.c | 12 ++++++++++++
>>   1 file changed, 12 insertions(+)
>>
>> diff --git a/arch/arm64/kernel/probes/kprobes.c b/arch/arm64/kernel/probes/kprobes.c
>> index 0c5d408afd95..8ab6104a4883 100644
>> --- a/arch/arm64/kernel/probes/kprobes.c
>> +++ b/arch/arm64/kernel/probes/kprobes.c
>> @@ -10,6 +10,7 @@
>>   
>>   #define pr_fmt(fmt) "kprobes: " fmt
>>   
>> +#include <linux/execmem.h>
>>   #include <linux/extable.h>
>>   #include <linux/kasan.h>
>>   #include <linux/kernel.h>
>> @@ -41,6 +42,17 @@ DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);
>>   static void __kprobes
>>   post_kprobe_handler(struct kprobe *, struct kprobe_ctlblk *, struct pt_regs *);
>>   
>> +void *alloc_insn_page(void)
>> +{
>> +	void *addr;
>> +
>> +	addr = execmem_alloc(EXECMEM_KPROBES, PAGE_SIZE);
>> +	if (!addr)
>> +		return NULL;
>> +	set_memory_rox((unsigned long)addr, 1);
>> +	return addr;
>> +}
> Why isn't execmem taking care of this? It looks to me like the
> execmem_cache_alloc() path calls set_memory_rox() but the
> execmem_vmalloc() path doesn't?

execmem_cache_alloc() is just called if execmem ROX cache is enabled, 
but it currently just supported by x86. Included Mike to this thread who 
is the author of execmem ROX cache.

>
> It feels a bit bizarre to me that we have to provide our own wrapper
> (which is identical to what s390 does). Also, how does alloc_insn_page()
> handle the direct map alias on x86?

x86 handles it via execmem ROX cache.

Thanks,
Yang

>
> Will

Re: [v2 PATCH] arm64: kprobes: call set_memory_rox() for kprobe page

Posted by Mike Rapoport 1 week, 4 days ago

On Thu, Sep 18, 2025 at 10:33:26AM -0700, Yang Shi wrote:
> 
> 
> On 9/18/25 10:26 AM, Will Deacon wrote:
> > On Thu, Sep 18, 2025 at 09:23:49AM -0700, Yang Shi wrote:
> > > The kprobe page is allocated by execmem allocator with ROX permission.
> > > It needs to call set_memory_rox() to set proper permission for the
> > > direct map too. It was missed.
> > > 
> > > Fixes: 10d5e97c1bf8 ("arm64: use PAGE_KERNEL_ROX directly in alloc_insn_page")
> > > Cc: <stable@vger.kernel.org>
> > > Signed-off-by: Yang Shi <yang@os.amperecomputing.com>
> > > Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
> > > ---
> > > v2: Separated the patch from BBML2 series since it is an orthogonal bug
> > >      fix per Ryan.
> > >      Fixed the variable name nit per Catalin.
> > >      Collected R-bs from Catalin.
> > > 
> > >   arch/arm64/kernel/probes/kprobes.c | 12 ++++++++++++
> > >   1 file changed, 12 insertions(+)
> > > 
> > > diff --git a/arch/arm64/kernel/probes/kprobes.c b/arch/arm64/kernel/probes/kprobes.c
> > > index 0c5d408afd95..8ab6104a4883 100644
> > > --- a/arch/arm64/kernel/probes/kprobes.c
> > > +++ b/arch/arm64/kernel/probes/kprobes.c
> > > @@ -10,6 +10,7 @@
> > >   #define pr_fmt(fmt) "kprobes: " fmt
> > > +#include <linux/execmem.h>
> > >   #include <linux/extable.h>
> > >   #include <linux/kasan.h>
> > >   #include <linux/kernel.h>
> > > @@ -41,6 +42,17 @@ DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);
> > >   static void __kprobes
> > >   post_kprobe_handler(struct kprobe *, struct kprobe_ctlblk *, struct pt_regs *);
> > > +void *alloc_insn_page(void)
> > > +{
> > > +	void *addr;
> > > +
> > > +	addr = execmem_alloc(EXECMEM_KPROBES, PAGE_SIZE);
> > > +	if (!addr)
> > > +		return NULL;
> > > +	set_memory_rox((unsigned long)addr, 1);
> > > +	return addr;
> > > +}
> > Why isn't execmem taking care of this? It looks to me like the
> > execmem_cache_alloc() path calls set_memory_rox() but the
> > execmem_vmalloc() path doesn't?

execmem_alloc() -> execmem_vmalloc() consolidated __vmalloc_node_range()
for executable allocations. Those also didn't update the linear map alias.

It could be added to execmem_vmalloc(), but as of now we don't have a way
for generic code to tell which set_memory method to call based on pgprot,
so making execmem_vmalloc() to deal with direct map alias is quite
involved.

It would be easier to just remove the direct map alias. It works on x86 so
I don't see what can possibly go wrong :)
 
> execmem_cache_alloc() is just called if execmem ROX cache is enabled, but it
> currently just supported by x86. Included Mike to this thread who is the
> author of execmem ROX cache.
> 
> > 
> > It feels a bit bizarre to me that we have to provide our own wrapper
> > (which is identical to what s390 does). Also, how does alloc_insn_page()
> > handle the direct map alias on x86?

s390 had its version of alloc_insn_page() long before execmem so there I
just replaced module_alloc() with exemem_alloc().

arm64 version of alloc_insn_page() didn't update the direct map before
execmem, so I overlooked this issue when I was converting arm64 to execmem.
 
> x86 handles it via execmem ROX cache.
> 
> Thanks,
> Yang
> 
> > 
> > Will
> 

-- 
Sincerely yours,
Mike.

Re: [v2 PATCH] arm64: kprobes: call set_memory_rox() for kprobe page

Posted by Yang Shi 1 week, 1 day ago


On 9/21/25 12:36 AM, Mike Rapoport wrote:
> On Thu, Sep 18, 2025 at 10:33:26AM -0700, Yang Shi wrote:
>>
>> On 9/18/25 10:26 AM, Will Deacon wrote:
>>> On Thu, Sep 18, 2025 at 09:23:49AM -0700, Yang Shi wrote:
>>>> The kprobe page is allocated by execmem allocator with ROX permission.
>>>> It needs to call set_memory_rox() to set proper permission for the
>>>> direct map too. It was missed.
>>>>
>>>> Fixes: 10d5e97c1bf8 ("arm64: use PAGE_KERNEL_ROX directly in alloc_insn_page")
>>>> Cc: <stable@vger.kernel.org>
>>>> Signed-off-by: Yang Shi <yang@os.amperecomputing.com>
>>>> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
>>>> ---
>>>> v2: Separated the patch from BBML2 series since it is an orthogonal bug
>>>>       fix per Ryan.
>>>>       Fixed the variable name nit per Catalin.
>>>>       Collected R-bs from Catalin.
>>>>
>>>>    arch/arm64/kernel/probes/kprobes.c | 12 ++++++++++++
>>>>    1 file changed, 12 insertions(+)
>>>>
>>>> diff --git a/arch/arm64/kernel/probes/kprobes.c b/arch/arm64/kernel/probes/kprobes.c
>>>> index 0c5d408afd95..8ab6104a4883 100644
>>>> --- a/arch/arm64/kernel/probes/kprobes.c
>>>> +++ b/arch/arm64/kernel/probes/kprobes.c
>>>> @@ -10,6 +10,7 @@
>>>>    #define pr_fmt(fmt) "kprobes: " fmt
>>>> +#include <linux/execmem.h>
>>>>    #include <linux/extable.h>
>>>>    #include <linux/kasan.h>
>>>>    #include <linux/kernel.h>
>>>> @@ -41,6 +42,17 @@ DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);
>>>>    static void __kprobes
>>>>    post_kprobe_handler(struct kprobe *, struct kprobe_ctlblk *, struct pt_regs *);
>>>> +void *alloc_insn_page(void)
>>>> +{
>>>> +	void *addr;
>>>> +
>>>> +	addr = execmem_alloc(EXECMEM_KPROBES, PAGE_SIZE);
>>>> +	if (!addr)
>>>> +		return NULL;
>>>> +	set_memory_rox((unsigned long)addr, 1);
>>>> +	return addr;
>>>> +}
>>> Why isn't execmem taking care of this? It looks to me like the
>>> execmem_cache_alloc() path calls set_memory_rox() but the
>>> execmem_vmalloc() path doesn't?
> execmem_alloc() -> execmem_vmalloc() consolidated __vmalloc_node_range()
> for executable allocations. Those also didn't update the linear map alias.
>
> It could be added to execmem_vmalloc(), but as of now we don't have a way
> for generic code to tell which set_memory method to call based on pgprot,
> so making execmem_vmalloc() to deal with direct map alias is quite
> involved.
>
> It would be easier to just remove the direct map alias. It works on x86 so
> I don't see what can possibly go wrong :)
>   
>> execmem_cache_alloc() is just called if execmem ROX cache is enabled, but it
>> currently just supported by x86. Included Mike to this thread who is the
>> author of execmem ROX cache.
>>
>>> It feels a bit bizarre to me that we have to provide our own wrapper
>>> (which is identical to what s390 does). Also, how does alloc_insn_page()
>>> handle the direct map alias on x86?
> s390 had its version of alloc_insn_page() long before execmem so there I
> just replaced module_alloc() with exemem_alloc().
>
> arm64 version of alloc_insn_page() didn't update the direct map before
> execmem, so I overlooked this issue when I was converting arm64 to execmem.

Thanks, Mike. It is not your fault. The set_memory_rox() was called in 
arm64's alloc_insn_page() before, but it was mistakenly removed by 
commit 10d5e97c1bf8 ("arm64: use PAGE_KERNEL_ROX directly in 
alloc_insn_page") before execmem.

Yang

>   
>> x86 handles it via execmem ROX cache.
>>
>> Thanks,
>> Yang
>>
>>> Will