Re: [PATCH RESEND] riscv: asid: Fixup stale TLB entry cause application crash

[Guo Ren]

Yes, thx for pointing that out.

On Tue, Nov 8, 2022 at 10:23 PM Conor Dooley <conor.dooley@xxxxxxxxxxxxx> wrote:
>
> On Tue, Nov 08, 2022 at 10:27:51AM +0000, Conor Dooley wrote:
> >
> >
> > On 8 November 2022 10:20:44 GMT, guoren@xxxxxxxxxx wrote:
> > >From: Guo Ren <guoren@xxxxxxxxxxxxxxxxx>
> > >
> > >After use_asid_allocator enabled, the userspace application will
> > >crash for stale tlb entry. Because only using cpumask_clear_cpu without
> > >local_flush_tlb_all couldn't guarantee CPU's tlb entries fresh. Then
> > >set_mm_asid would cause user space application get a stale value by
> > >the stale tlb entry, but set_mm_noasid is okay.
> > >
> > >Here is the symptom of the bug:
> > >unhandled signal 11 code 0x1 (coredump)
> > >   0x0000003fd6d22524 <+4>:     auipc   s0,0x70
> > >   0x0000003fd6d22528 <+8>:     ld      s0,-148(s0) # 0x3fd6d92490
> > >=> 0x0000003fd6d2252c <+12>:    ld      a5,0(s0)
> > >(gdb) i r s0
> > >s0          0x8082ed1cc3198b21       0x8082ed1cc3198b21
> > >(gdb) x/16 0x3fd6d92490
> > >0x3fd6d92490:   0xd80ac8a8      0x0000003f
> > >The core dump file shows that the value of register s0 is wrong, but the
> > >value in memory is right. This is because 'ld s0, -148(s0)' use a stale
> > >mapping entry in TLB and got a wrong value from a stale physical
> > >address.
> > >
> > >When task run on CPU0, the task loaded/speculative-loaded the value of
> > >address(0x3fd6d92490), and the first version of tlb mapping entry was
> > >PTWed into CPU0's tlb.
> > >When the task switched from CPU0 to CPU1 without local_tlb_flush_all
> > >(because of asid), the task happened to write a value on address
> > >(0x3fd6d92490). It caused do_page_fault -> wp_page_copy ->
> > >ptep_clear_flush -> ptep_get_and_clear & flush_tlb_page.
> > >The flush_tlb_page used mm_cpumask(mm) to determine which CPUs need
> > >tlb flush, but CPU0 had cleared the CPU0's mm_cpumask in previous switch_mm.
> > >So we only flushed the CPU1 tlb, and setted second version mapping
> > >of the pte. When the task switch from CPU1 to CPU0 again, CPU0 still used a
> > >stale tlb mapping entry which contained a wrong target physical address.
> > >When the task happened to read that value, the bug would be raised.
> > >
> > >Fixes: 65d4b9c53017 ("RISC-V: Implement ASID allocator")
> > >Signed-off-by: Guo Ren <guoren@xxxxxxxxxxxxxxxxx>
> > >Signed-off-by: Guo Ren <guoren@xxxxxxxxxx>
> > >Cc: Anup Patel <apatel@xxxxxxxxxxxxxxxx>
> > >Cc: Palmer Dabbelt <palmer@xxxxxxxxxxxx>
> > >---
> > > arch/riscv/mm/context.c | 4 +++-
> > > 1 file changed, 3 insertions(+), 1 deletion(-)
> > >
> > >diff --git a/arch/riscv/mm/context.c b/arch/riscv/mm/context.c
> > >index 7acbfbd14557..8ad6c2493e93 100644
> > >--- a/arch/riscv/mm/context.c
> > >+++ b/arch/riscv/mm/context.c
> > >@@ -317,7 +317,9 @@ void switch_mm(struct mm_struct *prev, struct mm_struct *next,
> > >      */
> > >     cpu = smp_processor_id();
> > >
> > >-    cpumask_clear_cpu(cpu, mm_cpumask(prev));
> > >+    if (!static_branch_unlikely(&use_asid_allocator))
> > >+            cpumask_clear_cpu(cpu, mm_cpumask(prev));
> > >+
> > >     cpumask_set_cpu(cpu, mm_cpumask(next));
> > >
> > >     set_mm(next, cpu);
> >
> > This is a completely different patch to what you already sent.
> > Why have you marked it RESEND rather than v2?
>
> In addition, it seems to break the build for the nommu defconfigs.



-- 
Best Regards
 Guo Ren