> -----Original Message----- > From: Miles Chen [mailto:miles.chen@xxxxxxxxxxxx] > Sent: Thursday, November 26, 2020 8:49 PM > To: Song Bao Hua (Barry Song) <song.bao.hua@xxxxxxxxxxxxx> > Cc: Alexey Dobriyan <adobriyan@xxxxxxxxx>; Andrew Morton > <akpm@xxxxxxxxxxxxxxxxxxxx>; linux-kernel@xxxxxxxxxxxxxxx; > linux-fsdevel@xxxxxxxxxxxxxxx; linux-mediatek@xxxxxxxxxxxxxxxxxxx; > wsd_upstream@xxxxxxxxxxxx > Subject: RE: [RESEND PATCH v1] proc: use untagged_addr() for pagemap_read > addresses > > On Thu, 2020-11-26 at 07:16 +0000, Song Bao Hua (Barry Song) wrote: > > > > > -----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. > > > > > I run arm64 devices. > If the tagged pointer is enabled, the ARM top-byte Ignore is also > enabled. It means the top-byte is always be ignored. > > I think the kernel should not break existing userspace program, so it's > better to handle the tagged user pointer in kernel. > > grep 'untag' mm -RnH to see existing examples. I see your point. But the existing examples such as gup etc are receiving an address from userspace. pagemap isn't getting an address, it is getting a file offset which should be figured out by userspace correctly. While we read a file, we should make sure the offset is in the range of the file length. > > > thanks, > Miles > > > > > > > /* > > > -- > > > 2.18.0 > > Thanks Barry
