On Mon, Mar 18, 2024 at 2:09 PM Johannes Weiner <hannes@xxxxxxxxxxx> wrote: > > On Mon, Mar 18, 2024 at 01:17:19PM -0700, Yosry Ahmed wrote: > > On Mon, Mar 18, 2024 at 11:00 AM Nhat Pham <nphamcs@xxxxxxxxx> wrote: > > > > > > On Mon, Mar 18, 2024 at 9:58 AM syzbot > > > <syzbot+adbc983a1588b7805de3@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote: > > > > > > > > Hello, > > > > > > > > syzbot found the following issue on: > > > > > > > > HEAD commit: e5eb28f6d1af Merge tag 'mm-nonmm-stable-2024-03-14-09-36' .. > > > > git tree: upstream > > > > console output: https://syzkaller.appspot.com/x/log.txt?x=13043abe180000 > > > > kernel config: https://syzkaller.appspot.com/x/.config?x=19bb57c23dffc38e > > > > dashboard link: https://syzkaller.appspot.com/bug?extid=adbc983a1588b7805de3 > > > > compiler: arm-linux-gnueabi-gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40 > > > > userspace arch: arm > > > > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1706d231180000 > > > > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=13ba7959180000 > > > > > > > > Downloadable assets: > > > > disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/8ead8862021c/non_bootable_disk-e5eb28f6.raw.xz > > > > vmlinux: https://storage.googleapis.com/syzbot-assets/0a7371c63ff2/vmlinux-e5eb28f6.xz > > > > kernel image: https://storage.googleapis.com/syzbot-assets/7539441b4add/zImage-e5eb28f6.xz > > > > > > > > IMPORTANT: if you fix the issue, please add the following tag to the commit: > > > > Reported-by: syzbot+adbc983a1588b7805de3@xxxxxxxxxxxxxxxxxxxxxxxxx > > > > > > > > ------------[ cut here ]------------ > > > > kernel BUG at include/linux/scatterlist.h:187! > > > > > > Looks like the provided buffer is invalid: > > > > > > #ifdef CONFIG_DEBUG_SG > > > BUG_ON(!virt_addr_valid(buf)); > > > #endif > > > > > > which is "src" from: > > > > > > sg_init_one(&input, src, entry->length); > > > > > > Looking at the surrounding code and recent history, there's this > > > commit that stands out: > > > > > > mm/zswap: remove the memcpy if acomp is not sleepable > > > (sha: 270700dd06ca41a4779c19eb46608f076bb7d40e) > > > > > > which has the effect of, IIUC, using the zpool mapped memory directly > > > as src, instead of acomp_ctx->buffer (which was previously the case, > > > as zsmalloc was not sleepable). > > > > > > This might not necessarily be a bug with that commit itself, but might > > > have revealed another bug elsewhere. > > > > > > Anyway, cc-ing the author, Barry Song, to fact check me :) Will take a > > > closer look later. > > > > I am not a highmem expert, but the reproducer has CONFIG_HIGHMEM=y, > > and it seems like zs_map_object() may return a highmem address if the > > compressed object is entirely in a single page to avoid copying to a > > buffer: > > > > if (off + class->size <= PAGE_SIZE) { > > /* this object is contained entirely within a page */ > > area->vm_addr = kmap_atomic(page); > > ret = area->vm_addr + off; > > goto out; > > } > > > > The virt_addr_valid() check seems to indicate that we expect a direct > > map address in sg_init_one(), right? > > If the page is highmem, kmap_atomic() establishes a temporary mapping > to it in the direct map, such that we have a legit kernel pointer to > the memory. Otherwise the memcpy() in zswap also wouldn't work... Am I > missing something? IIUC kmap_atomic() establishes a mapping in the kernel portion of the address space, but not a direct map mapping (i.e. not a linear mapping), right? Does virt_addr_valid() check for addresses being in the kernel portion of the address space, or it being a linear mapping? I thought it checks for the latter.
