> -----Original Message----- > From: Miles Chen [mailto:miles.chen@xxxxxxxxxxxx] > Sent: Monday, November 23, 2020 7:39 PM > To: Alexey Dobriyan <adobriyan@xxxxxxxxx>; Andrew Morton > <akpm@xxxxxxxxxxxxxxxxxxxx> > Cc: linux-kernel@xxxxxxxxxxxxxxx; linux-fsdevel@xxxxxxxxxxxxxxx; > linux-mediatek@xxxxxxxxxxxxxxxxxxx; wsd_upstream@xxxxxxxxxxxx; Miles > Chen <miles.chen@xxxxxxxxxxxx> > Subject: [RESEND PATCH v1] 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. > > My test code is baed on [1]: > > 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://github.com/stressapptest/stressapptest/blob/master/src/os.cc#L158 > > Signed-off-by: Miles Chen <miles.chen@xxxxxxxxxxxx> > --- > fs/proc/task_mmu.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c > index 217aa2705d5d..e9a70f7ee515 100644 > --- a/fs/proc/task_mmu.c > +++ b/fs/proc/task_mmu.c > @@ -1599,11 +1599,11 @@ static ssize_t pagemap_read(struct file *file, char > __user *buf, > > src = *ppos; > svpfn = src / PM_ENTRY_BYTES; > - start_vaddr = svpfn << PAGE_SHIFT; > + start_vaddr = untagged_addr(svpfn << PAGE_SHIFT); > end_vaddr = mm->task_size; > > /* watch out for wraparound */ > - if (svpfn > mm->task_size >> PAGE_SHIFT) > + if (start_vaddr > mm->task_size) > start_vaddr = end_vaddr; Wouldn't the untag be done by the user reading pagemap file? With this patch, even users pass an illegal address, for example, users put a tag on a virtual address which hasn't really a tag, they will still get the right pagemap. > > /* > -- > 2.18.0 Thanks Barry
