[v2] proc: use untagged_addr() for pagemap_read addresses
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Message ID 20201127050738.14440-1-miles.chen@mediatek.com
State In Next
Commit d7ab2c274d36ea95dca99f559fad964c5fbca7e4
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  • [v2] proc: use untagged_addr() for pagemap_read addresses
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Commit Message

Miles Chen Nov. 27, 2020, 5:07 a.m. UTC
When we try to visit the pagemap of a tagged userspace pointer, we find
that the start_vaddr is not correct because of the tag.
To fix it, we should untag the usespace pointers in pagemap_read().

I tested with 5.10-rc4 and the issue remains.

Explaination from Catalin in [1]:

"
Arguably, that's a user-space bug since tagged file offsets were never
supported. In this case it's not even a tag at bit 56 as per the arm64
tagged address ABI but rather down to bit 47. You could say that the
problem is caused by the C library (malloc()) or whoever created the
tagged vaddr and passed it to this function. It's not a kernel
regression as we've never supported it.

Now, pagemap is a special case where the offset is usually not generated
as a classic file offset but rather derived by shifting a user virtual
address. I guess we can make a concession for pagemap (only) and allow
such offset with the tag at bit (56 - PAGE_SHIFT + 3).
"

My test code is baed on [2]:

A userspace pointer which has been tagged by 0xb4: 0xb400007662f541c8

=== userspace program ===

uint64 OsLayer::VirtualToPhysical(void *vaddr) {
	uint64 frame, paddr, pfnmask, pagemask;
	int pagesize = sysconf(_SC_PAGESIZE);
	off64_t off = ((uintptr_t)vaddr) / pagesize * 8; // off = 0xb400007662f541c8 / pagesize * 8 = 0x5a00003b317aa0
	int fd = open(kPagemapPath, O_RDONLY);
	...

	if (lseek64(fd, off, SEEK_SET) != off || read(fd, &frame, 8) != 8) {
		int err = errno;
		string errtxt = ErrorString(err);
		if (fd >= 0)
			close(fd);
		return 0;
	}
...
}

=== kernel fs/proc/task_mmu.c ===

static ssize_t pagemap_read(struct file *file, char __user *buf,
		size_t count, loff_t *ppos)
{
	...
	src = *ppos;
	svpfn = src / PM_ENTRY_BYTES; // svpfn == 0xb400007662f54
	start_vaddr = svpfn << PAGE_SHIFT; // start_vaddr == 0xb400007662f54000
	end_vaddr = mm->task_size;

	/* watch out for wraparound */
	// svpfn == 0xb400007662f54
	// (mm->task_size >> PAGE) == 0x8000000
	if (svpfn > mm->task_size >> PAGE_SHIFT) // the condition is true because of the tag 0xb4
		start_vaddr = end_vaddr;

	ret = 0;
	while (count && (start_vaddr < end_vaddr)) { // we cannot visit correct entry because start_vaddr is set to end_vaddr
		int len;
		unsigned long end;
		...
	}
	...
}

[1] https://lore.kernel.org/patchwork/patch/1343258/
[2] https://github.com/stressapptest/stressapptest/blob/master/src/os.cc#L158

Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Andrey Konovalov <andreyknvl@google.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Vincenzo Frascino <vincenzo.frascino@arm.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Marco Elver <elver@google.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Eric W. Biederman <ebiederm@xmission.com>
Cc: Song Bao Hua (Barry Song) <song.bao.hua@hisilicon.com>
Cc: stable@vger.kernel.org # v5.4-
Signed-off-by: Miles Chen <miles.chen@mediatek.com>

---

Change since v1:

1. Follow Eirc's and Catalin's suggestion to avoid overflow
2. Cc to stable v5.4-
3. add explaination from Catalin to the commit message
---
 fs/proc/task_mmu.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

Comments

Catalin Marinas Dec. 3, 2020, 11:30 a.m. UTC | #1
On Fri, Nov 27, 2020 at 01:07:38PM +0800, Miles Chen wrote:
> Cc: Will Deacon <will.deacon@arm.com>

That should be will@kernel.org.

> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> index 217aa2705d5d..92b277388f05 100644
> --- a/fs/proc/task_mmu.c
> +++ b/fs/proc/task_mmu.c
> @@ -1599,11 +1599,15 @@ static ssize_t pagemap_read(struct file *file, char __user *buf,
>  
>  	src = *ppos;
>  	svpfn = src / PM_ENTRY_BYTES;
> -	start_vaddr = svpfn << PAGE_SHIFT;
>  	end_vaddr = mm->task_size;
>  
>  	/* watch out for wraparound */
> -	if (svpfn > mm->task_size >> PAGE_SHIFT)
> +	start_vaddr = end_vaddr;
> +	if (svpfn < (ULONG_MAX >> PAGE_SHIFT))

Does this need to be strict less-than? I think a less-than or equal
would work better.

> +		start_vaddr = untagged_addr(svpfn << PAGE_SHIFT);
> +
> +	/* Ensure the address is inside the task */
> +	if (start_vaddr > mm->task_size)
>  		start_vaddr = end_vaddr;

Otherwise the logic looks fine to me. With the above:

Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Vincenzo Frascino Dec. 3, 2020, 11:45 a.m. UTC | #2
Hi Miles,

On 11/27/20 5:07 AM, Miles Chen wrote:
> When we try to visit the pagemap of a tagged userspace pointer, we find
> that the start_vaddr is not correct because of the tag.
> To fix it, we should untag the usespace pointers in pagemap_read().
> 

Nit: s/usespace/userspace/ (please search and replace all occurrences :) )

> I tested with 5.10-rc4 and the issue remains.
> 
> Explaination from Catalin in [1]:
>

Nit: s/Explaination/Explanation/ (please search and replace all occurrences :) )

> "
> Arguably, that's a user-space bug since tagged file offsets were never
> supported. In this case it's not even a tag at bit 56 as per the arm64
> tagged address ABI but rather down to bit 47. You could say that the
> problem is caused by the C library (malloc()) or whoever created the
> tagged vaddr and passed it to this function. It's not a kernel
> regression as we've never supported it.
> 
> Now, pagemap is a special case where the offset is usually not generated
> as a classic file offset but rather derived by shifting a user virtual
> address. I guess we can make a concession for pagemap (only) and allow
> such offset with the tag at bit (56 - PAGE_SHIFT + 3).
> "
> 
> My test code is baed on [2]:

Nit: s/baed/based/ (please search and replace all occurrences :) )

[...]

> ---
>  fs/proc/task_mmu.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> index 217aa2705d5d..92b277388f05 100644
> --- a/fs/proc/task_mmu.c
> +++ b/fs/proc/task_mmu.c
> @@ -1599,11 +1599,15 @@ static ssize_t pagemap_read(struct file *file, char __user *buf,
>  
>  	src = *ppos;
>  	svpfn = src / PM_ENTRY_BYTES;
> -	start_vaddr = svpfn << PAGE_SHIFT;
>  	end_vaddr = mm->task_size;
>  
>  	/* watch out for wraparound */
> -	if (svpfn > mm->task_size >> PAGE_SHIFT)
> +	start_vaddr = end_vaddr;
> +	if (svpfn < (ULONG_MAX >> PAGE_SHIFT))

It seems that 'svpfn' should be less-then-equal (<=) '(ULONG_MAX >>
PAGE_SHIFT)'. Is there any specific reason why this is not the case?

> +		start_vaddr = untagged_addr(svpfn << PAGE_SHIFT);
> +
> +	/* Ensure the address is inside the task */
> +	if (start_vaddr > mm->task_size)
>  		start_vaddr = end_vaddr;
>  
>  	/*
> 

Otherwise:

Reviewed-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
Miles Chen Dec. 4, 2020, 1:33 a.m. UTC | #3
On Thu, 2020-12-03 at 11:45 +0000, Vincenzo Frascino wrote:
> Hi Miles,
> 
> On 11/27/20 5:07 AM, Miles Chen wrote:
> > When we try to visit the pagemap of a tagged userspace pointer, we find
> > that the start_vaddr is not correct because of the tag.
> > To fix it, we should untag the usespace pointers in pagemap_read().
> > 
> 
> Nit: s/usespace/userspace/ (please search and replace all occurrences :) )
> 
> > I tested with 5.10-rc4 and the issue remains.
> > 
> > Explaination from Catalin in [1]:
> >
> 
> Nit: s/Explaination/Explanation/ (please search and replace all occurrences :) )

thanks, I will fix this and push v3
> 
> > "
> > Arguably, that's a user-space bug since tagged file offsets were never
> > supported. In this case it's not even a tag at bit 56 as per the arm64
> > tagged address ABI but rather down to bit 47. You could say that the
> > problem is caused by the C library (malloc()) or whoever created the
> > tagged vaddr and passed it to this function. It's not a kernel
> > regression as we've never supported it.
> > 
> > Now, pagemap is a special case where the offset is usually not generated
> > as a classic file offset but rather derived by shifting a user virtual
> > address. I guess we can make a concession for pagemap (only) and allow
> > such offset with the tag at bit (56 - PAGE_SHIFT + 3).
> > "
> > 
> > My test code is baed on [2]:
> 
> Nit: s/baed/based/ (please search and replace all occurrences :) )

thanks, I will fix this and push v3



Miles
> 
> [...]
> 
> > ---
> >  fs/proc/task_mmu.c | 8 ++++++--
> >  1 file changed, 6 insertions(+), 2 deletions(-)
> > 
> > diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> > index 217aa2705d5d..92b277388f05 100644
> > --- a/fs/proc/task_mmu.c
> > +++ b/fs/proc/task_mmu.c
> > @@ -1599,11 +1599,15 @@ static ssize_t pagemap_read(struct file *file, char __user *buf,
> >  
> >  	src = *ppos;
> >  	svpfn = src / PM_ENTRY_BYTES;
> > -	start_vaddr = svpfn << PAGE_SHIFT;
> >  	end_vaddr = mm->task_size;
> >  
> >  	/* watch out for wraparound */
> > -	if (svpfn > mm->task_size >> PAGE_SHIFT)
> > +	start_vaddr = end_vaddr;
> > +	if (svpfn < (ULONG_MAX >> PAGE_SHIFT))
> 
> It seems that 'svpfn' should be less-then-equal (<=) '(ULONG_MAX >>
> PAGE_SHIFT)'. Is there any specific reason why this is not the case?
> 
> > +		start_vaddr = untagged_addr(svpfn << PAGE_SHIFT);
> > +
> > +	/* Ensure the address is inside the task */
> > +	if (start_vaddr > mm->task_size)
> >  		start_vaddr = end_vaddr;
> >  
> >  	/*
> > 
> 
> Otherwise:
> 
> Reviewed-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
>
Miles Chen Dec. 4, 2020, 1:34 a.m. UTC | #4
On Thu, 2020-12-03 at 11:30 +0000, Catalin Marinas wrote:
> On Fri, Nov 27, 2020 at 01:07:38PM +0800, Miles Chen wrote:
> > Cc: Will Deacon <will.deacon@arm.com>
> 
> That should be will@kernel.org.

ok, I will fix it and submit v3
> 
> > diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> > index 217aa2705d5d..92b277388f05 100644
> > --- a/fs/proc/task_mmu.c
> > +++ b/fs/proc/task_mmu.c
> > @@ -1599,11 +1599,15 @@ static ssize_t pagemap_read(struct file *file, char __user *buf,
> >  
> >  	src = *ppos;
> >  	svpfn = src / PM_ENTRY_BYTES;
> > -	start_vaddr = svpfn << PAGE_SHIFT;
> >  	end_vaddr = mm->task_size;
> >  
> >  	/* watch out for wraparound */
> > -	if (svpfn > mm->task_size >> PAGE_SHIFT)
> > +	start_vaddr = end_vaddr;
> > +	if (svpfn < (ULONG_MAX >> PAGE_SHIFT))
> 
> Does this need to be strict less-than? I think a less-than or equal
> would work better.

Thanks, I will fix it and submit v3.
> 
> > +		start_vaddr = untagged_addr(svpfn << PAGE_SHIFT);
> > +
> > +	/* Ensure the address is inside the task */
> > +	if (start_vaddr > mm->task_size)
> >  		start_vaddr = end_vaddr;
> 
> Otherwise the logic looks fine to me. With the above:
> 
> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>

Patch
diff mbox series

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 217aa2705d5d..92b277388f05 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -1599,11 +1599,15 @@  static ssize_t pagemap_read(struct file *file, char __user *buf,
 
 	src = *ppos;
 	svpfn = src / PM_ENTRY_BYTES;
-	start_vaddr = svpfn << PAGE_SHIFT;
 	end_vaddr = mm->task_size;
 
 	/* watch out for wraparound */
-	if (svpfn > mm->task_size >> PAGE_SHIFT)
+	start_vaddr = end_vaddr;
+	if (svpfn < (ULONG_MAX >> PAGE_SHIFT))
+		start_vaddr = untagged_addr(svpfn << PAGE_SHIFT);
+
+	/* Ensure the address is inside the task */
+	if (start_vaddr > mm->task_size)
 		start_vaddr = end_vaddr;
 
 	/*