Re: [PATCH v2] proc: use untagged_addr() for pagemap_read addresses
On Thu, 2020-12-03 at 11:30 +, Catalin Marinas wrote: > On Fri, Nov 27, 2020 at 01:07:38PM +0800, Miles Chen wrote: > > Cc: Will Deacon > > That should be w...@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
Re: [PATCH v2] proc: use untagged_addr() for pagemap_read addresses
On Thu, 2020-12-03 at 11:45 +, 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 >
Re: [PATCH v2] proc: use untagged_addr() for pagemap_read addresses
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 -- Regards, Vincenzo
Re: [PATCH v2] proc: use untagged_addr() for pagemap_read addresses
On Fri, Nov 27, 2020 at 01:07:38PM +0800, Miles Chen wrote: > Cc: Will Deacon That should be w...@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
[PATCH v2] proc: use untagged_addr() for pagemap_read addresses
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: 0xb47662f541c8
=== 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 =
0xb47662f541c8 / pagesize * 8 = 0x5a3b317aa0
int fd = open(kPagemapPath, O_RDONLY);
...
if (lseek64(fd, off, SEEK_SET) != off || read(fd, , 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 == 0xb47662f54
start_vaddr = svpfn << PAGE_SHIFT; // start_vaddr == 0xb47662f54000
end_vaddr = mm->task_size;
/* watch out for wraparound */
// svpfn == 0xb47662f54
// (mm->task_size >> PAGE) == 0x800
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
Cc: Alexey Dobriyan
Cc: Andrey Konovalov
Cc: Alexander Potapenko
Cc: Vincenzo Frascino
Cc: Andrey Ryabinin
Cc: Catalin Marinas
Cc: Dmitry Vyukov
Cc: Marco Elver
Cc: Will Deacon
Cc: Eric W. Biederman
Cc: Song Bao Hua (Barry Song)
Cc: sta...@vger.kernel.org # v5.4-
Signed-off-by: Miles Chen
---
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(-)
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;
/*
--
2.18.0
