On Fri, 2020-11-27 at 19:52 -0800, akpm@xxxxxxxxxxxxxxxxxxxx wrote: > The patch titled > Subject: proc: use untagged_addr() for pagemap_read addresses > has been added to the -mm tree. Its filename is > proc-use-untagged_addr-for-pagemap_read-addresses.patch > > This patch should soon appear at > https://ozlabs.org/~akpm/mmots/broken-out/proc-use-untagged_addr-for-pagemap_read-addresses.patch > and later at > https://ozlabs.org/~akpm/mmotm/broken-out/proc-use-untagged_addr-for-pagemap_read-addresses.patch > > Before you just go and hit "reply", please: > a) Consider who else should be cc'ed > b) Prefer to cc a suitable mailing list as well > c) Ideally: find the original patch on the mailing list and do a > reply-to-all to that, adding suitable additional cc's > > *** Remember to use Documentation/process/submit-checklist.rst when testing your code *** > > The -mm tree is included into linux-next and is updated > there every 3-4 working days Sorry for bothering, I checked the next-20201201 tag and the patch in next-20201201 is [1], but there is a overflow issue in [1] so I submitted v2 [2]. We should take [2], right? (the patch in this email is [2] but the patch in next-20201201 is [1]) [1] https://lore.kernel.org/patchwork/patch/1343258/ [1] https://lore.kernel.org/patchwork/patch/1345874/ > > ------------------------------------------------------ > From: Miles Chen <miles.chen@xxxxxxxxxxxx> > Subject: 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. > > Explanation 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 > > Link: https://lkml.kernel.org/r/20201127050738.14440-1-miles.chen@xxxxxxxxxxxx > Signed-off-by: Miles Chen <miles.chen@xxxxxxxxxxxx> > Cc: Alexey Dobriyan <adobriyan@xxxxxxxxx> > Cc: Andrey Konovalov <andreyknvl@xxxxxxxxxx> > Cc: Alexander Potapenko <glider@xxxxxxxxxx> > Cc: Vincenzo Frascino <vincenzo.frascino@xxxxxxx> > Cc: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx> > Cc: Catalin Marinas <catalin.marinas@xxxxxxx> > Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx> > Cc: Marco Elver <elver@xxxxxxxxxx> > Cc: Will Deacon <will.deacon@xxxxxxx> > Cc: Eric W. Biederman <ebiederm@xxxxxxxxxxxx> > Cc: Song Bao Hua (Barry Song) <song.bao.hua@xxxxxxxxxxxxx> > Cc: <stable@xxxxxxxxxxxxxxx> [5.4+] > Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> > --- > > fs/proc/task_mmu.c | 8 ++++++-- > 1 file changed, 6 insertions(+), 2 deletions(-) > > --- a/fs/proc/task_mmu.c~proc-use-untagged_addr-for-pagemap_read-addresses > +++ a/fs/proc/task_mmu.c > @@ -1599,11 +1599,15 @@ static ssize_t pagemap_read(struct file > > 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; > > /* > _ > > Patches currently in -mm which might be from miles.chen@xxxxxxxxxxxx are > > proc-use-untagged_addr-for-pagemap_read-addresses.patch >
