[PATCH v3 1/2] riscv: Make VM_WRITE imply VM_READ

[PATCH v3 1/2] riscv: Make VM_WRITE imply VM_READ

[Andrew Bresticker]

RISC-V does not presently have write-only mappings as that PTE bit pattern
is considered reserved in the privileged spec, so allow handling of read
faults in VMAs that have VM_WRITE without VM_READ in order to be consistent
with other architectures that have similar limitations.

Reviewed-by: Atish Patra <atishp@rivosinc.com>
Signed-off-by: Andrew Bresticker <abrestic@rivosinc.com>
---
 arch/riscv/mm/fault.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/riscv/mm/fault.c b/arch/riscv/mm/fault.c
index f2fbd1400b7c..d86f7cebd4a7 100644
--- a/arch/riscv/mm/fault.c
+++ b/arch/riscv/mm/fault.c
@@ -184,7 +184,8 @@ static inline bool access_error(unsigned long cause, struct vm_area_struct *vma)
 		}
 		break;
 	case EXC_LOAD_PAGE_FAULT:
-		if (!(vma->vm_flags & VM_READ)) {
+		/* Write implies read */
+		if (!(vma->vm_flags & (VM_READ | VM_WRITE))) {
 			return true;
 		}
 		break;
-- 
2.25.1

[PATCH v3 1/2] riscv: Make VM_WRITE imply VM_READ

[Andrew Bresticker]

RISC-V does not presently have write-only mappings as that PTE bit pattern
is considered reserved in the privileged spec, so allow handling of read
faults in VMAs that have VM_WRITE without VM_READ in order to be consistent
with other architectures that have similar limitations.

Reviewed-by: Atish Patra <atishp@rivosinc.com>
Signed-off-by: Andrew Bresticker <abrestic@rivosinc.com>
---
 arch/riscv/mm/fault.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/riscv/mm/fault.c b/arch/riscv/mm/fault.c
index f2fbd1400b7c..d86f7cebd4a7 100644
--- a/arch/riscv/mm/fault.c
+++ b/arch/riscv/mm/fault.c
@@ -184,7 +184,8 @@ static inline bool access_error(unsigned long cause, struct vm_area_struct *vma)
 		}
 		break;
 	case EXC_LOAD_PAGE_FAULT:
-		if (!(vma->vm_flags & VM_READ)) {
+		/* Write implies read */
+		if (!(vma->vm_flags & (VM_READ | VM_WRITE))) {
 			return true;
 		}
 		break;
-- 
2.25.1


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[PATCH v3 2/2] riscv: Allow PROT_WRITE-only mmap()

[Andrew Bresticker]

Commit 2139619bcad7 ("riscv: mmap with PROT_WRITE but no PROT_READ is
invalid") made mmap() return EINVAL if PROT_WRITE was set wihtout
PROT_READ with the justification that a write-only PTE is considered a
reserved PTE permission bit pattern in the privileged spec. This check
is unnecessary since we let VM_WRITE imply VM_READ on RISC-V, and it is
inconsistent with other architectures that don't support write-only PTEs,
creating a potential software portability issue. Just remove the check
altogether and let PROT_WRITE imply PROT_READ as is the case on other
architectures.

Note that this also allows PROT_WRITE|PROT_EXEC mappings which were
disallowed prior to the aforementioned commit; PROT_READ is implied in
such mappings as well.

Fixes: 2139619bcad7 ("riscv: mmap with PROT_WRITE but no PROT_READ is invalid")
Reviewed-by: Atish Patra <atishp@rivosinc.com>
Signed-off-by: Andrew Bresticker <abrestic@rivosinc.com>
---
v1 -> v2: Update access_error() to account for write-implies-read
v2 -> v3: Separate into two commits
---
 arch/riscv/kernel/sys_riscv.c | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/arch/riscv/kernel/sys_riscv.c b/arch/riscv/kernel/sys_riscv.c
index 571556bb9261..5d3f2fbeb33c 100644
--- a/arch/riscv/kernel/sys_riscv.c
+++ b/arch/riscv/kernel/sys_riscv.c
@@ -18,9 +18,6 @@ static long riscv_sys_mmap(unsigned long addr, unsigned long len,
 	if (unlikely(offset & (~PAGE_MASK >> page_shift_offset)))
 		return -EINVAL;
 
-	if (unlikely((prot & PROT_WRITE) && !(prot & PROT_READ)))
-		return -EINVAL;
-
 	return ksys_mmap_pgoff(addr, len, prot, flags, fd,
 			       offset >> (PAGE_SHIFT - page_shift_offset));
 }
-- 
2.25.1

[PATCH v3 2/2] riscv: Allow PROT_WRITE-only mmap()

[Andrew Bresticker]

Commit 2139619bcad7 ("riscv: mmap with PROT_WRITE but no PROT_READ is
invalid") made mmap() return EINVAL if PROT_WRITE was set wihtout
PROT_READ with the justification that a write-only PTE is considered a
reserved PTE permission bit pattern in the privileged spec. This check
is unnecessary since we let VM_WRITE imply VM_READ on RISC-V, and it is
inconsistent with other architectures that don't support write-only PTEs,
creating a potential software portability issue. Just remove the check
altogether and let PROT_WRITE imply PROT_READ as is the case on other
architectures.

Note that this also allows PROT_WRITE|PROT_EXEC mappings which were
disallowed prior to the aforementioned commit; PROT_READ is implied in
such mappings as well.

Fixes: 2139619bcad7 ("riscv: mmap with PROT_WRITE but no PROT_READ is invalid")
Reviewed-by: Atish Patra <atishp@rivosinc.com>
Signed-off-by: Andrew Bresticker <abrestic@rivosinc.com>
---
v1 -> v2: Update access_error() to account for write-implies-read
v2 -> v3: Separate into two commits
---
 arch/riscv/kernel/sys_riscv.c | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/arch/riscv/kernel/sys_riscv.c b/arch/riscv/kernel/sys_riscv.c
index 571556bb9261..5d3f2fbeb33c 100644
--- a/arch/riscv/kernel/sys_riscv.c
+++ b/arch/riscv/kernel/sys_riscv.c
@@ -18,9 +18,6 @@ static long riscv_sys_mmap(unsigned long addr, unsigned long len,
 	if (unlikely(offset & (~PAGE_MASK >> page_shift_offset)))
 		return -EINVAL;
 
-	if (unlikely((prot & PROT_WRITE) && !(prot & PROT_READ)))
-		return -EINVAL;
-
 	return ksys_mmap_pgoff(addr, len, prot, flags, fd,
 			       offset >> (PAGE_SHIFT - page_shift_offset));
 }
-- 
2.25.1


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Re: [PATCH v3 2/2] riscv: Allow PROT_WRITE-only mmap()

[Conor.Dooley]

On 09/09/2022 22:27, Andrew Bresticker wrote:
> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
> 
> Commit 2139619bcad7 ("riscv: mmap with PROT_WRITE but no PROT_READ is
> invalid") made mmap() return EINVAL if PROT_WRITE was set wihtout
> PROT_READ with the justification that a write-only PTE is considered a
> reserved PTE permission bit pattern in the privileged spec. This check
> is unnecessary since we let VM_WRITE imply VM_READ on RISC-V, and it is
> inconsistent with other architectures that don't support write-only PTEs,
> creating a potential software portability issue. Just remove the check
> altogether and let PROT_WRITE imply PROT_READ as is the case on other
> architectures.
> 
> Note that this also allows PROT_WRITE|PROT_EXEC mappings which were
> disallowed prior to the aforementioned commit; PROT_READ is implied in
> such mappings as well.
> 
> Fixes: 2139619bcad7 ("riscv: mmap with PROT_WRITE but no PROT_READ is invalid")

For the naive members of the audience such as myself, this patch
came after a non-fixes patch in the series. What is the dependence
of this patch on the other one (if any)?
Thanks,
Conor.

> Reviewed-by: Atish Patra <atishp@rivosinc.com>
> Signed-off-by: Andrew Bresticker <abrestic@rivosinc.com>
> ---
> v1 -> v2: Update access_error() to account for write-implies-read
> v2 -> v3: Separate into two commits
> ---
>  arch/riscv/kernel/sys_riscv.c | 3 ---
>  1 file changed, 3 deletions(-)
> 
> diff --git a/arch/riscv/kernel/sys_riscv.c b/arch/riscv/kernel/sys_riscv.c
> index 571556bb9261..5d3f2fbeb33c 100644
> --- a/arch/riscv/kernel/sys_riscv.c
> +++ b/arch/riscv/kernel/sys_riscv.c
> @@ -18,9 +18,6 @@ static long riscv_sys_mmap(unsigned long addr, unsigned long len,
>         if (unlikely(offset & (~PAGE_MASK >> page_shift_offset)))
>                 return -EINVAL;
> 
> -       if (unlikely((prot & PROT_WRITE) && !(prot & PROT_READ)))
> -               return -EINVAL;
> -
>         return ksys_mmap_pgoff(addr, len, prot, flags, fd,
>                                offset >> (PAGE_SHIFT - page_shift_offset));
>  }
> --
> 2.25.1
> 
> 
> _______________________________________________
> linux-riscv mailing list
> linux-riscv@lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-riscv

Re: [PATCH v3 2/2] riscv: Allow PROT_WRITE-only mmap()

[Conor.Dooley]

On 09/09/2022 22:27, Andrew Bresticker wrote:
> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
> 
> Commit 2139619bcad7 ("riscv: mmap with PROT_WRITE but no PROT_READ is
> invalid") made mmap() return EINVAL if PROT_WRITE was set wihtout
> PROT_READ with the justification that a write-only PTE is considered a
> reserved PTE permission bit pattern in the privileged spec. This check
> is unnecessary since we let VM_WRITE imply VM_READ on RISC-V, and it is
> inconsistent with other architectures that don't support write-only PTEs,
> creating a potential software portability issue. Just remove the check
> altogether and let PROT_WRITE imply PROT_READ as is the case on other
> architectures.
> 
> Note that this also allows PROT_WRITE|PROT_EXEC mappings which were
> disallowed prior to the aforementioned commit; PROT_READ is implied in
> such mappings as well.
> 
> Fixes: 2139619bcad7 ("riscv: mmap with PROT_WRITE but no PROT_READ is invalid")

For the naive members of the audience such as myself, this patch
came after a non-fixes patch in the series. What is the dependence
of this patch on the other one (if any)?
Thanks,
Conor.

> Reviewed-by: Atish Patra <atishp@rivosinc.com>
> Signed-off-by: Andrew Bresticker <abrestic@rivosinc.com>
> ---
> v1 -> v2: Update access_error() to account for write-implies-read
> v2 -> v3: Separate into two commits
> ---
>  arch/riscv/kernel/sys_riscv.c | 3 ---
>  1 file changed, 3 deletions(-)
> 
> diff --git a/arch/riscv/kernel/sys_riscv.c b/arch/riscv/kernel/sys_riscv.c
> index 571556bb9261..5d3f2fbeb33c 100644
> --- a/arch/riscv/kernel/sys_riscv.c
> +++ b/arch/riscv/kernel/sys_riscv.c
> @@ -18,9 +18,6 @@ static long riscv_sys_mmap(unsigned long addr, unsigned long len,
>         if (unlikely(offset & (~PAGE_MASK >> page_shift_offset)))
>                 return -EINVAL;
> 
> -       if (unlikely((prot & PROT_WRITE) && !(prot & PROT_READ)))
> -               return -EINVAL;
> -
>         return ksys_mmap_pgoff(addr, len, prot, flags, fd,
>                                offset >> (PAGE_SHIFT - page_shift_offset));
>  }
> --
> 2.25.1
> 
> 
> _______________________________________________
> linux-riscv mailing list
> linux-riscv@lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-riscv

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Re: [PATCH v3 2/2] riscv: Allow PROT_WRITE-only mmap()

[Andrew Bresticker]

On Thu, Sep 15, 2022 at 12:56 PM <Conor.Dooley@microchip.com> wrote:
>
> On 09/09/2022 22:27, Andrew Bresticker wrote:
> > EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
> >
> > Commit 2139619bcad7 ("riscv: mmap with PROT_WRITE but no PROT_READ is
> > invalid") made mmap() return EINVAL if PROT_WRITE was set wihtout
> > PROT_READ with the justification that a write-only PTE is considered a
> > reserved PTE permission bit pattern in the privileged spec. This check
> > is unnecessary since we let VM_WRITE imply VM_READ on RISC-V, and it is
> > inconsistent with other architectures that don't support write-only PTEs,
> > creating a potential software portability issue. Just remove the check
> > altogether and let PROT_WRITE imply PROT_READ as is the case on other
> > architectures.
> >
> > Note that this also allows PROT_WRITE|PROT_EXEC mappings which were
> > disallowed prior to the aforementioned commit; PROT_READ is implied in
> > such mappings as well.
> >
> > Fixes: 2139619bcad7 ("riscv: mmap with PROT_WRITE but no PROT_READ is invalid")
>
> For the naive members of the audience such as myself, this patch
> came after a non-fixes patch in the series. What is the dependence
> of this patch on the other one (if any)?

This patch is dependent on the first. Happy to re-spin with a "Fixes"
tag on the first patch (or maybe Palmer can add when applying).

-Andrew

> Thanks,
> Conor.
>
> > Reviewed-by: Atish Patra <atishp@rivosinc.com>
> > Signed-off-by: Andrew Bresticker <abrestic@rivosinc.com>
> > ---
> > v1 -> v2: Update access_error() to account for write-implies-read
> > v2 -> v3: Separate into two commits
> > ---
> >  arch/riscv/kernel/sys_riscv.c | 3 ---
> >  1 file changed, 3 deletions(-)
> >
> > diff --git a/arch/riscv/kernel/sys_riscv.c b/arch/riscv/kernel/sys_riscv.c
> > index 571556bb9261..5d3f2fbeb33c 100644
> > --- a/arch/riscv/kernel/sys_riscv.c
> > +++ b/arch/riscv/kernel/sys_riscv.c
> > @@ -18,9 +18,6 @@ static long riscv_sys_mmap(unsigned long addr, unsigned long len,
> >         if (unlikely(offset & (~PAGE_MASK >> page_shift_offset)))
> >                 return -EINVAL;
> >
> > -       if (unlikely((prot & PROT_WRITE) && !(prot & PROT_READ)))
> > -               return -EINVAL;
> > -
> >         return ksys_mmap_pgoff(addr, len, prot, flags, fd,
> >                                offset >> (PAGE_SHIFT - page_shift_offset));
> >  }
> > --
> > 2.25.1
> >
> >
> > _______________________________________________
> > linux-riscv mailing list
> > linux-riscv@lists.infradead.org
> > http://lists.infradead.org/mailman/listinfo/linux-riscv
>

Re: [PATCH v3 2/2] riscv: Allow PROT_WRITE-only mmap()

[Andrew Bresticker]

On Thu, Sep 15, 2022 at 12:56 PM <Conor.Dooley@microchip.com> wrote:
>
> On 09/09/2022 22:27, Andrew Bresticker wrote:
> > EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
> >
> > Commit 2139619bcad7 ("riscv: mmap with PROT_WRITE but no PROT_READ is
> > invalid") made mmap() return EINVAL if PROT_WRITE was set wihtout
> > PROT_READ with the justification that a write-only PTE is considered a
> > reserved PTE permission bit pattern in the privileged spec. This check
> > is unnecessary since we let VM_WRITE imply VM_READ on RISC-V, and it is
> > inconsistent with other architectures that don't support write-only PTEs,
> > creating a potential software portability issue. Just remove the check
> > altogether and let PROT_WRITE imply PROT_READ as is the case on other
> > architectures.
> >
> > Note that this also allows PROT_WRITE|PROT_EXEC mappings which were
> > disallowed prior to the aforementioned commit; PROT_READ is implied in
> > such mappings as well.
> >
> > Fixes: 2139619bcad7 ("riscv: mmap with PROT_WRITE but no PROT_READ is invalid")
>
> For the naive members of the audience such as myself, this patch
> came after a non-fixes patch in the series. What is the dependence
> of this patch on the other one (if any)?

This patch is dependent on the first. Happy to re-spin with a "Fixes"
tag on the first patch (or maybe Palmer can add when applying).

-Andrew

> Thanks,
> Conor.
>
> > Reviewed-by: Atish Patra <atishp@rivosinc.com>
> > Signed-off-by: Andrew Bresticker <abrestic@rivosinc.com>
> > ---
> > v1 -> v2: Update access_error() to account for write-implies-read
> > v2 -> v3: Separate into two commits
> > ---
> >  arch/riscv/kernel/sys_riscv.c | 3 ---
> >  1 file changed, 3 deletions(-)
> >
> > diff --git a/arch/riscv/kernel/sys_riscv.c b/arch/riscv/kernel/sys_riscv.c
> > index 571556bb9261..5d3f2fbeb33c 100644
> > --- a/arch/riscv/kernel/sys_riscv.c
> > +++ b/arch/riscv/kernel/sys_riscv.c
> > @@ -18,9 +18,6 @@ static long riscv_sys_mmap(unsigned long addr, unsigned long len,
> >         if (unlikely(offset & (~PAGE_MASK >> page_shift_offset)))
> >                 return -EINVAL;
> >
> > -       if (unlikely((prot & PROT_WRITE) && !(prot & PROT_READ)))
> > -               return -EINVAL;
> > -
> >         return ksys_mmap_pgoff(addr, len, prot, flags, fd,
> >                                offset >> (PAGE_SHIFT - page_shift_offset));
> >  }
> > --
> > 2.25.1
> >
> >
> > _______________________________________________
> > linux-riscv mailing list
> > linux-riscv@lists.infradead.org
> > http://lists.infradead.org/mailman/listinfo/linux-riscv
>

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Re: [PATCH v3 2/2] riscv: Allow PROT_WRITE-only mmap()

[Conor.Dooley]

On 15/09/2022 18:27, Andrew Bresticker wrote:
> On Thu, Sep 15, 2022 at 12:56 PM <Conor.Dooley@microchip.com> wrote:
>>
>> On 09/09/2022 22:27, Andrew Bresticker wrote:
>>> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
>>>
>>> Commit 2139619bcad7 ("riscv: mmap with PROT_WRITE but no PROT_READ is
>>> invalid") made mmap() return EINVAL if PROT_WRITE was set wihtout
>>> PROT_READ with the justification that a write-only PTE is considered a
>>> reserved PTE permission bit pattern in the privileged spec. This check
>>> is unnecessary since we let VM_WRITE imply VM_READ on RISC-V, and it is
>>> inconsistent with other architectures that don't support write-only PTEs,
>>> creating a potential software portability issue. Just remove the check
>>> altogether and let PROT_WRITE imply PROT_READ as is the case on other
>>> architectures.
>>>
>>> Note that this also allows PROT_WRITE|PROT_EXEC mappings which were
>>> disallowed prior to the aforementioned commit; PROT_READ is implied in
>>> such mappings as well.
>>>
>>> Fixes: 2139619bcad7 ("riscv: mmap with PROT_WRITE but no PROT_READ is invalid")
>>
>> For the naive members of the audience such as myself, this patch
>> came after a non-fixes patch in the series. What is the dependence
>> of this patch on the other one (if any)?
> 
> This patch is dependent on the first. Happy to re-spin with a "Fixes"
> tag on the first patch (or maybe Palmer can add when applying).

If it is a fix, then it should have a fixes tag. If it's cosmetic reorg
to make the fix easier then no & it should be moved after the fix. If
it is neither then you should prob mention it in the cover or under the
--- /shrug

Thanks,
Conor.

>>> Reviewed-by: Atish Patra <atishp@rivosinc.com>
>>> Signed-off-by: Andrew Bresticker <abrestic@rivosinc.com>
>>> ---
>>> v1 -> v2: Update access_error() to account for write-implies-read
>>> v2 -> v3: Separate into two commits
>>> ---
>>>  arch/riscv/kernel/sys_riscv.c | 3 ---
>>>  1 file changed, 3 deletions(-)
>>>
>>> diff --git a/arch/riscv/kernel/sys_riscv.c b/arch/riscv/kernel/sys_riscv.c
>>> index 571556bb9261..5d3f2fbeb33c 100644
>>> --- a/arch/riscv/kernel/sys_riscv.c
>>> +++ b/arch/riscv/kernel/sys_riscv.c
>>> @@ -18,9 +18,6 @@ static long riscv_sys_mmap(unsigned long addr, unsigned long len,
>>>         if (unlikely(offset & (~PAGE_MASK >> page_shift_offset)))
>>>                 return -EINVAL;
>>>
>>> -       if (unlikely((prot & PROT_WRITE) && !(prot & PROT_READ)))
>>> -               return -EINVAL;
>>> -
>>>         return ksys_mmap_pgoff(addr, len, prot, flags, fd,
>>>                                offset >> (PAGE_SHIFT - page_shift_offset));
>>>  }
>>> --
>>> 2.25.1
>>>
>>>
>>> _______________________________________________
>>> linux-riscv mailing list
>>> linux-riscv@lists.infradead.org
>>> http://lists.infradead.org/mailman/listinfo/linux-riscv
>>

Re: [PATCH v3 2/2] riscv: Allow PROT_WRITE-only mmap()

[Conor.Dooley]

On 15/09/2022 18:27, Andrew Bresticker wrote:
> On Thu, Sep 15, 2022 at 12:56 PM <Conor.Dooley@microchip.com> wrote:
>>
>> On 09/09/2022 22:27, Andrew Bresticker wrote:
>>> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
>>>
>>> Commit 2139619bcad7 ("riscv: mmap with PROT_WRITE but no PROT_READ is
>>> invalid") made mmap() return EINVAL if PROT_WRITE was set wihtout
>>> PROT_READ with the justification that a write-only PTE is considered a
>>> reserved PTE permission bit pattern in the privileged spec. This check
>>> is unnecessary since we let VM_WRITE imply VM_READ on RISC-V, and it is
>>> inconsistent with other architectures that don't support write-only PTEs,
>>> creating a potential software portability issue. Just remove the check
>>> altogether and let PROT_WRITE imply PROT_READ as is the case on other
>>> architectures.
>>>
>>> Note that this also allows PROT_WRITE|PROT_EXEC mappings which were
>>> disallowed prior to the aforementioned commit; PROT_READ is implied in
>>> such mappings as well.
>>>
>>> Fixes: 2139619bcad7 ("riscv: mmap with PROT_WRITE but no PROT_READ is invalid")
>>
>> For the naive members of the audience such as myself, this patch
>> came after a non-fixes patch in the series. What is the dependence
>> of this patch on the other one (if any)?
> 
> This patch is dependent on the first. Happy to re-spin with a "Fixes"
> tag on the first patch (or maybe Palmer can add when applying).

If it is a fix, then it should have a fixes tag. If it's cosmetic reorg
to make the fix easier then no & it should be moved after the fix. If
it is neither then you should prob mention it in the cover or under the
--- /shrug

Thanks,
Conor.

>>> Reviewed-by: Atish Patra <atishp@rivosinc.com>
>>> Signed-off-by: Andrew Bresticker <abrestic@rivosinc.com>
>>> ---
>>> v1 -> v2: Update access_error() to account for write-implies-read
>>> v2 -> v3: Separate into two commits
>>> ---
>>>  arch/riscv/kernel/sys_riscv.c | 3 ---
>>>  1 file changed, 3 deletions(-)
>>>
>>> diff --git a/arch/riscv/kernel/sys_riscv.c b/arch/riscv/kernel/sys_riscv.c
>>> index 571556bb9261..5d3f2fbeb33c 100644
>>> --- a/arch/riscv/kernel/sys_riscv.c
>>> +++ b/arch/riscv/kernel/sys_riscv.c
>>> @@ -18,9 +18,6 @@ static long riscv_sys_mmap(unsigned long addr, unsigned long len,
>>>         if (unlikely(offset & (~PAGE_MASK >> page_shift_offset)))
>>>                 return -EINVAL;
>>>
>>> -       if (unlikely((prot & PROT_WRITE) && !(prot & PROT_READ)))
>>> -               return -EINVAL;
>>> -
>>>         return ksys_mmap_pgoff(addr, len, prot, flags, fd,
>>>                                offset >> (PAGE_SHIFT - page_shift_offset));
>>>  }
>>> --
>>> 2.25.1
>>>
>>>
>>> _______________________________________________
>>> linux-riscv mailing list
>>> linux-riscv@lists.infradead.org
>>> http://lists.infradead.org/mailman/listinfo/linux-riscv
>>
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Re: [PATCH v3 2/2] riscv: Allow PROT_WRITE-only mmap()

[Vivian Wang]

On 9/16/22 01:40, Conor.Dooley@microchip.com wrote:
> On 15/09/2022 18:27, Andrew Bresticker wrote:
>> On Thu, Sep 15, 2022 at 12:56 PM <Conor.Dooley@microchip.com> wrote:
>>> On 09/09/2022 22:27, Andrew Bresticker wrote:
>>>> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
>>>>
>>>> Commit 2139619bcad7 ("riscv: mmap with PROT_WRITE but no PROT_READ is
>>>> invalid") made mmap() return EINVAL if PROT_WRITE was set wihtout
>>>> PROT_READ with the justification that a write-only PTE is considered a
>>>> reserved PTE permission bit pattern in the privileged spec. This check
>>>> is unnecessary since we let VM_WRITE imply VM_READ on RISC-V, and it is
>>>> inconsistent with other architectures that don't support write-only PTEs,
>>>> creating a potential software portability issue. Just remove the check
>>>> altogether and let PROT_WRITE imply PROT_READ as is the case on other
>>>> architectures.
>>>>
>>>> Note that this also allows PROT_WRITE|PROT_EXEC mappings which were
>>>> disallowed prior to the aforementioned commit; PROT_READ is implied in
>>>> such mappings as well.
>>>>
>>>> Fixes: 2139619bcad7 ("riscv: mmap with PROT_WRITE but no PROT_READ is invalid")
>>> For the naive members of the audience such as myself, this patch
>>> came after a non-fixes patch in the series. What is the dependence
>>> of this patch on the other one (if any)?
>> This patch is dependent on the first. Happy to re-spin with a "Fixes"
>> tag on the first patch (or maybe Palmer can add when applying).
> If it is a fix, then it should have a fixes tag. If it's cosmetic reorg
> to make the fix easier then no & it should be moved after the fix. If
> it is neither then you should prob mention it in the cover or under the
> --- /shrug

Basically what happens fixes-wise is that patch 1 fixes the original
problem in a different way, and patch 2 undoes the previous patch (with
small additional fixes). IMO this needs a cover to explain what's going
on to those who missed the v1 and v2 discussion thread.

v1 here: https://lore.kernel.org/all/20220908170133.1159747-1-abrestic@rivosinc.com

Thanks,
dram

> Thanks,
> Conor.
>
>>>> Reviewed-by: Atish Patra <atishp@rivosinc.com>
>>>> Signed-off-by: Andrew Bresticker <abrestic@rivosinc.com>
>>>> ---
>>>> v1 -> v2: Update access_error() to account for write-implies-read
>>>> v2 -> v3: Separate into two commits
>>>> ---
>>>>  arch/riscv/kernel/sys_riscv.c | 3 ---
>>>>  1 file changed, 3 deletions(-)
>>>>
>>>> diff --git a/arch/riscv/kernel/sys_riscv.c b/arch/riscv/kernel/sys_riscv.c
>>>> index 571556bb9261..5d3f2fbeb33c 100644
>>>> --- a/arch/riscv/kernel/sys_riscv.c
>>>> +++ b/arch/riscv/kernel/sys_riscv.c
>>>> @@ -18,9 +18,6 @@ static long riscv_sys_mmap(unsigned long addr, unsigned long len,
>>>>         if (unlikely(offset & (~PAGE_MASK >> page_shift_offset)))
>>>>                 return -EINVAL;
>>>>
>>>> -       if (unlikely((prot & PROT_WRITE) && !(prot & PROT_READ)))
>>>> -               return -EINVAL;
>>>> -
>>>>         return ksys_mmap_pgoff(addr, len, prot, flags, fd,
>>>>                                offset >> (PAGE_SHIFT - page_shift_offset));
>>>>  }
>>>> --
>>>> 2.25.1
>>>>
>>>>
>>>> _______________________________________________
>>>> linux-riscv mailing list
>>>> linux-riscv@lists.infradead.org
>>>> http://lists.infradead.org/mailman/listinfo/linux-riscv

Re: [PATCH v3 2/2] riscv: Allow PROT_WRITE-only mmap()

[Vivian Wang]

On 9/16/22 01:40, Conor.Dooley@microchip.com wrote:
> On 15/09/2022 18:27, Andrew Bresticker wrote:
>> On Thu, Sep 15, 2022 at 12:56 PM <Conor.Dooley@microchip.com> wrote:
>>> On 09/09/2022 22:27, Andrew Bresticker wrote:
>>>> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
>>>>
>>>> Commit 2139619bcad7 ("riscv: mmap with PROT_WRITE but no PROT_READ is
>>>> invalid") made mmap() return EINVAL if PROT_WRITE was set wihtout
>>>> PROT_READ with the justification that a write-only PTE is considered a
>>>> reserved PTE permission bit pattern in the privileged spec. This check
>>>> is unnecessary since we let VM_WRITE imply VM_READ on RISC-V, and it is
>>>> inconsistent with other architectures that don't support write-only PTEs,
>>>> creating a potential software portability issue. Just remove the check
>>>> altogether and let PROT_WRITE imply PROT_READ as is the case on other
>>>> architectures.
>>>>
>>>> Note that this also allows PROT_WRITE|PROT_EXEC mappings which were
>>>> disallowed prior to the aforementioned commit; PROT_READ is implied in
>>>> such mappings as well.
>>>>
>>>> Fixes: 2139619bcad7 ("riscv: mmap with PROT_WRITE but no PROT_READ is invalid")
>>> For the naive members of the audience such as myself, this patch
>>> came after a non-fixes patch in the series. What is the dependence
>>> of this patch on the other one (if any)?
>> This patch is dependent on the first. Happy to re-spin with a "Fixes"
>> tag on the first patch (or maybe Palmer can add when applying).
> If it is a fix, then it should have a fixes tag. If it's cosmetic reorg
> to make the fix easier then no & it should be moved after the fix. If
> it is neither then you should prob mention it in the cover or under the
> --- /shrug

Basically what happens fixes-wise is that patch 1 fixes the original
problem in a different way, and patch 2 undoes the previous patch (with
small additional fixes). IMO this needs a cover to explain what's going
on to those who missed the v1 and v2 discussion thread.

v1 here: https://lore.kernel.org/all/20220908170133.1159747-1-abrestic@rivosinc.com

Thanks,
dram

> Thanks,
> Conor.
>
>>>> Reviewed-by: Atish Patra <atishp@rivosinc.com>
>>>> Signed-off-by: Andrew Bresticker <abrestic@rivosinc.com>
>>>> ---
>>>> v1 -> v2: Update access_error() to account for write-implies-read
>>>> v2 -> v3: Separate into two commits
>>>> ---
>>>>  arch/riscv/kernel/sys_riscv.c | 3 ---
>>>>  1 file changed, 3 deletions(-)
>>>>
>>>> diff --git a/arch/riscv/kernel/sys_riscv.c b/arch/riscv/kernel/sys_riscv.c
>>>> index 571556bb9261..5d3f2fbeb33c 100644
>>>> --- a/arch/riscv/kernel/sys_riscv.c
>>>> +++ b/arch/riscv/kernel/sys_riscv.c
>>>> @@ -18,9 +18,6 @@ static long riscv_sys_mmap(unsigned long addr, unsigned long len,
>>>>         if (unlikely(offset & (~PAGE_MASK >> page_shift_offset)))
>>>>                 return -EINVAL;
>>>>
>>>> -       if (unlikely((prot & PROT_WRITE) && !(prot & PROT_READ)))
>>>> -               return -EINVAL;
>>>> -
>>>>         return ksys_mmap_pgoff(addr, len, prot, flags, fd,
>>>>                                offset >> (PAGE_SHIFT - page_shift_offset));
>>>>  }
>>>> --
>>>> 2.25.1
>>>>
>>>>
>>>> _______________________________________________
>>>> linux-riscv mailing list
>>>> linux-riscv@lists.infradead.org
>>>> http://lists.infradead.org/mailman/listinfo/linux-riscv

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