@@ -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;
/*
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 userspace 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 based 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 Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Alexey Dobriyan <adobriyan@gmail.com> Cc: Andrey Konovalov <andreyknvl@google.com> Cc: Alexander Potapenko <glider@google.com> Cc: Vincenzo Frascino <vincenzo.frascino@arm.com> Cc: Andrey Ryabinin <aryabinin@virtuozzo.com> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Dmitry Vyukov <dvyukov@google.com> Cc: Marco Elver <elver@google.com> Cc: Will Deacon <will@kernel.org> Cc: Eric W. Biederman <ebiederm@xmission.com> Cc: Song Bao Hua (Barry Song) <song.bao.hua@hisilicon.com> Cc: stable@vger.kernel.org # v5.4- Signed-off-by: Miles Chen <miles.chen@mediatek.com> Reviewed-by: Vincenzo Frascino <vincenzo.frascino@arm.com> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com> --- 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 Change since v2: 1. replace less-than with less-than or equal 2. Fix bad spelling in commit message 3. Fix will's email address --- fs/proc/task_mmu.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-)