linux-kernel - Re: [PATCH v9 01/26] mm: helper `is_shadow_stack

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Message-ID: <Z6aMuuXMQAu7Tcvm@debug.ba.rivosinc.com>
Date: Fri, 7 Feb 2025 14:44:10 -0800
From: Deepak Gupta <debug@...osinc.com>
To: Vlastimil Babka <vbabka@...e.cz>
Cc: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
	Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
	"H. Peter Anvin" <hpa@...or.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Liam R. Howlett" <Liam.Howlett@...cle.com>,
	Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
	Paul Walmsley <paul.walmsley@...ive.com>,
	Palmer Dabbelt <palmer@...belt.com>,
	Albert Ou <aou@...s.berkeley.edu>, Conor Dooley <conor@...nel.org>,
	Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
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Subject: Re: [PATCH v9 01/26] mm: helper `is_shadow_stack_vma` to check
 shadow stack vma

On Fri, Feb 07, 2025 at 10:27:10AM +0100, Vlastimil Babka wrote:
>On 2/5/25 02:21, Deepak Gupta wrote:
>> VM_SHADOW_STACK (alias to VM_HIGH_ARCH_5) is used to encode shadow stack
>
>I see that arm GCS uses VM_HIGH_ARCH_6.

Stale commit message. I thought I had fixed it.
Sorry about that, will fix it.

>
>> VMA on three architectures (x86 shadow stack, arm GCS and RISC-V shadow
>
>And RISC-V doesn't define it at all, not even in this patchset, or did I
>miss it somewhere?
>
>> stack). In case architecture doesn't implement shadow stack, it's VM_NONE
>> Introducing a helper `is_shadow_stack_vma` to determine shadow stack vma
>> or not.
>
>This looks like an unfinished sentence. As if it was to continue with "...
>will allow us to ..." what?
>
>I'm not against a helper but this changelog is rather confusing and also
>code in arch/x86 and arch/arm64 isn't converted to the helper but testing
>VM_SHADOW_STACK still.

Yes I didn't pay attention during rebase, will update the commit message.
>
>> Signed-off-by: Deepak Gupta <debug@...osinc.com>
>> Reviewed-by: Mark Brown <broonie@...nel.org>
>> ---
>>  mm/gup.c  |  2 +-
>>  mm/mmap.c |  2 +-
>>  mm/vma.h  | 10 +++++++---
>>  3 files changed, 9 insertions(+), 5 deletions(-)
>>
>> diff --git a/mm/gup.c b/mm/gup.c
>> index 3883b307780e..8c64f3ff34ab 100644
>> --- a/mm/gup.c
>> +++ b/mm/gup.c
>> @@ -1291,7 +1291,7 @@ static int check_vma_flags(struct vm_area_struct *vma, unsigned long gup_flags)
>>  		    !writable_file_mapping_allowed(vma, gup_flags))
>>  			return -EFAULT;
>>
>> -		if (!(vm_flags & VM_WRITE) || (vm_flags & VM_SHADOW_STACK)) {
>> +		if (!(vm_flags & VM_WRITE) || is_shadow_stack_vma(vm_flags)) {
>>  			if (!(gup_flags & FOLL_FORCE))
>>  				return -EFAULT;
>>  			/*
>> diff --git a/mm/mmap.c b/mm/mmap.c
>> index cda01071c7b1..7b6be4eec35d 100644
>> --- a/mm/mmap.c
>> +++ b/mm/mmap.c
>> @@ -648,7 +648,7 @@ SYSCALL_DEFINE1(old_mmap, struct mmap_arg_struct __user *, arg)
>>   */
>>  static inline unsigned long stack_guard_placement(vm_flags_t vm_flags)
>>  {
>> -	if (vm_flags & VM_SHADOW_STACK)
>> +	if (is_shadow_stack_vma(vm_flags))
>>  		return PAGE_SIZE;
>>
>>  	return 0;
>> diff --git a/mm/vma.h b/mm/vma.h
>> index a2e8710b8c47..47482a25f5c3 100644
>> --- a/mm/vma.h
>> +++ b/mm/vma.h
>> @@ -278,7 +278,7 @@ static inline struct vm_area_struct *vma_prev_limit(struct vma_iterator *vmi,
>>  }
>>
>>  /*
>> - * These three helpers classifies VMAs for virtual memory accounting.
>> + * These four helpers classifies VMAs for virtual memory accounting.
>>   */
>>
>>  /*
>> @@ -289,6 +289,11 @@ static inline bool is_exec_mapping(vm_flags_t flags)
>>  	return (flags & (VM_EXEC | VM_WRITE | VM_STACK)) == VM_EXEC;
>>  }
>>
>> +static inline bool is_shadow_stack_vma(vm_flags_t vm_flags)
>> +{
>> +	return !!(vm_flags & VM_SHADOW_STACK);
>> +}
>> +
>>  /*
>>   * Stack area (including shadow stacks)
>>   *
>> @@ -297,7 +302,7 @@ static inline bool is_exec_mapping(vm_flags_t flags)
>>   */
>>  static inline bool is_stack_mapping(vm_flags_t flags)
>>  {
>> -	return ((flags & VM_STACK) == VM_STACK) || (flags & VM_SHADOW_STACK);
>> +	return ((flags & VM_STACK) == VM_STACK) || is_shadow_stack_vma(flags);
>>  }
>>
>>  /*
>> @@ -308,7 +313,6 @@ static inline bool is_data_mapping(vm_flags_t flags)
>>  	return (flags & (VM_WRITE | VM_SHARED | VM_STACK)) == VM_WRITE;
>>  }
>>
>> -
>>  static inline void vma_iter_config(struct vma_iterator *vmi,
>>  		unsigned long index, unsigned long last)
>>  {
>>
>