On Thu, Mar 20, 2025 at 6:40 PM Andrey Ryabinin <ryabinin.a.a@xxxxxxxxx> wrote: > > On Tue, Feb 18, 2025 at 9:19 AM Maciej Wieczor-Retman > <maciej.wieczor-retman@xxxxxxxxx> wrote: > > > > The problem presented here is related to NUMA systems and tag-based > > KASAN mode. Getting to it can be explained in the following points: > > > > 1. A new chunk is created with pcpu_create_chunk() and > > vm_structs are allocated. On systems with one NUMA node only > > one is allocated, but with more NUMA nodes at least a second > > one will be allocated too. > > > > 2. chunk->base_addr is assigned the modified value of > > vms[0]->addr and thus inherits the tag of this allocated > > structure. > > > > 3. In pcpu_alloc() for each possible cpu pcpu_chunk_addr() is > > executed which calculates per cpu pointers that correspond to > > the vms structure addresses. The calculations are based on > > adding an offset from a table to chunk->base_addr. > > > > Here the problem presents itself since for addresses based on vms[1] and > > up, the tag will be different than the ones based on vms[0] (base_addr). > > The tag mismatch happens and an error is reported. > > > > Reset the base_addr tag, since it will disable tag checks for pointers > > derived arithmetically from base_addr that would inherit its tag. > > > > Signed-off-by: Maciej Wieczor-Retman <maciej.wieczor-retman@xxxxxxxxx> > > --- > > mm/percpu-vm.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/mm/percpu-vm.c b/mm/percpu-vm.c > > index cd69caf6aa8d..e13750d804f7 100644 > > --- a/mm/percpu-vm.c > > +++ b/mm/percpu-vm.c > > @@ -347,7 +347,7 @@ static struct pcpu_chunk *pcpu_create_chunk(gfp_t gfp) > > } > > > > chunk->data = vms; > > - chunk->base_addr = vms[0]->addr - pcpu_group_offsets[0]; > > + chunk->base_addr = kasan_reset_tag(vms[0]->addr) - pcpu_group_offsets[0]; > > This looks like a generic tags mode bug. I mean that arm64 is also > affected by this. > I assume it just wasn't noticed before because arm64 with multiple > NUMAs are much less common. > > With this change tag-mode KASAN won't be able to catch bugus accesses > to pcpu areas. > I'm thinking it would be better to fix this on the pcpu_get_vm_areas() > area side by replacing > this > for (area = 0; area < nr_vms; area++) > vms[area]->addr = kasan_unpoison_vmalloc(vms[area]->addr, > vms[area]->size, > KASAN_VMALLOC_PROT_NORMAL); > > with something like > kasan_unpoison_vmap_areas(vms, nr_vms); > which will unpoison all areas using the same tag. > > Thoughts? Just a side note: KASAN doesn't have proper handling of the percpu areas anyway, I even had to remove a related test; see [1] and [2]. So I think for now we can go with the simplest/consistent solution that prevents false-positives, whichever that solution is. [1] https://bugzilla.kernel.org/show_bug.cgi?id=215019 [2] https://bugzilla.kernel.org/show_bug.cgi?id=215758
