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@xxxxxxx> >
