[PATCH V2] riscv: asid: Fixup stale TLB entry cause application crash

[PATCH V2] riscv: asid: Fixup stale TLB entry cause application crash

[guoren]

From: Guo Ren <guoren@linux.alibaba.com>

After use_asid_allocator is enabled, the userspace application will
crash by stale TLB entries. Because only using cpumask_clear_cpu without
local_flush_tlb_all couldn't guarantee CPU's TLB entries were fresh.
Then set_mm_asid would cause the user space application to get a stale
value by 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 /2x 0x3fd6d92490
0x3fd6d92490:   0xd80ac8a8      0x0000003f
The core dump file shows that register s0 is wrong, but the value in
memory is correct. Because 'ld s0, -148(s0)' used a stale mapping entry
in TLB and got a wrong result from an incorrect physical address.

When the task ran on CPU0, which loaded/speculative-loaded the value of
address(0x3fd6d92490), then the first version of the mapping entry was
PTWed into CPU0's TLB.
When the task switched from CPU0 to CPU1 (No local_tlb_flush_all here by
asid), it happened to write a value on the 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 the previous
switch_mm. So we only flushed the CPU1 TLB and set the second version
mapping of the PTE. When the task switched from CPU1 to CPU0 again, CPU0
still used a stale TLB mapping entry which contained a wrong target
physical address. It raised a bug when the task happened to read that
value.

The solution is to keep all CPUs' footmarks of cpumask(mm) in switch_mm,
which could prevent losing pieces of stuff during TLB flush.

Fixes: 65d4b9c53017 ("RISC-V: Implement ASID allocator")
Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
Signed-off-by: Guo Ren <guoren@kernel.org>
Cc: Anup Patel <apatel@ventanamicro.com>
Cc: Palmer Dabbelt <palmer@rivosinc.com>
---
Changes in v2:
 - Fixup nommu compile problem (Thx Conor, Also Reported-by: kernel
   test robot <lkp@intel.com>)
 - Keep cpumask_clear_cpu for noasid
---
 arch/riscv/mm/context.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/arch/riscv/mm/context.c b/arch/riscv/mm/context.c
index 7acbfbd14557..f58e4b211595 100644
--- a/arch/riscv/mm/context.c
+++ b/arch/riscv/mm/context.c
@@ -317,7 +317,11 @@ void switch_mm(struct mm_struct *prev, struct mm_struct *next,
 	 */
 	cpu = smp_processor_id();
 
-	cpumask_clear_cpu(cpu, mm_cpumask(prev));
+#ifdef CONFIG_MMU
+	if (!static_branch_unlikely(&use_asid_allocator))
+#endif
+		cpumask_clear_cpu(cpu, mm_cpumask(prev));
+
 	cpumask_set_cpu(cpu, mm_cpumask(next));
 
 	set_mm(next, cpu);
-- 
2.36.1

Re: [PATCH V2] riscv: asid: Fixup stale TLB entry cause application crash

[Andrew Jones]

On Wed, Nov 09, 2022 at 12:40:56AM -0500, guoren@kernel.org wrote:
> From: Guo Ren <guoren@linux.alibaba.com>
> 
> After use_asid_allocator is enabled, the userspace application will
> crash by stale TLB entries. Because only using cpumask_clear_cpu without
> local_flush_tlb_all couldn't guarantee CPU's TLB entries were fresh.
> Then set_mm_asid would cause the user space application to get a stale
> value by 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 /2x 0x3fd6d92490
> 0x3fd6d92490:   0xd80ac8a8      0x0000003f
> The core dump file shows that register s0 is wrong, but the value in
> memory is correct. Because 'ld s0, -148(s0)' used a stale mapping entry
> in TLB and got a wrong result from an incorrect physical address.
> 
> When the task ran on CPU0, which loaded/speculative-loaded the value of
> address(0x3fd6d92490), then the first version of the mapping entry was
> PTWed into CPU0's TLB.
> When the task switched from CPU0 to CPU1 (No local_tlb_flush_all here by
> asid), it happened to write a value on the 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 the previous
> switch_mm. So we only flushed the CPU1 TLB and set the second version
> mapping of the PTE. When the task switched from CPU1 to CPU0 again, CPU0
> still used a stale TLB mapping entry which contained a wrong target
> physical address. It raised a bug when the task happened to read that
> value.
> 
> The solution is to keep all CPUs' footmarks of cpumask(mm) in switch_mm,
> which could prevent losing pieces of stuff during TLB flush.
> 
> Fixes: 65d4b9c53017 ("RISC-V: Implement ASID allocator")
> Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
> Signed-off-by: Guo Ren <guoren@kernel.org>
> Cc: Anup Patel <apatel@ventanamicro.com>
> Cc: Palmer Dabbelt <palmer@rivosinc.com>
> ---
> Changes in v2:
>  - Fixup nommu compile problem (Thx Conor, Also Reported-by: kernel
>    test robot <lkp@intel.com>)
>  - Keep cpumask_clear_cpu for noasid
> ---
>  arch/riscv/mm/context.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/riscv/mm/context.c b/arch/riscv/mm/context.c
> index 7acbfbd14557..f58e4b211595 100644
> --- a/arch/riscv/mm/context.c
> +++ b/arch/riscv/mm/context.c
> @@ -317,7 +317,11 @@ void switch_mm(struct mm_struct *prev, struct mm_struct *next,
>  	 */
>  	cpu = smp_processor_id();
>  
> -	cpumask_clear_cpu(cpu, mm_cpumask(prev));
> +#ifdef CONFIG_MMU
> +	if (!static_branch_unlikely(&use_asid_allocator))
> +#endif

That's not very pretty. Can't we just do the following, instead?

diff --git a/arch/riscv/mm/context.c b/arch/riscv/mm/context.c
index 7acbfbd14557..ace419761e31 100644
--- a/arch/riscv/mm/context.c
+++ b/arch/riscv/mm/context.c
@@ -16,10 +16,11 @@
 #include <asm/cacheflush.h>
 #include <asm/mmu_context.h>

-#ifdef CONFIG_MMU

 DEFINE_STATIC_KEY_FALSE(use_asid_allocator);

+#ifdef CONFIG_MMU
+
 static unsigned long asid_bits;
 static unsigned long num_asids;
 static unsigned long asid_mask;


Thanks,
drew

> +		cpumask_clear_cpu(cpu, mm_cpumask(prev));
> +
>  	cpumask_set_cpu(cpu, mm_cpumask(next));
>  
>  	set_mm(next, cpu);
> -- 
> 2.36.1
> 
> 
> _______________________________________________
> linux-riscv mailing list
> linux-riscv@lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-riscv

Re: [PATCH V2] riscv: asid: Fixup stale TLB entry cause application crash

[Guo Ren]

On Wed, Nov 9, 2022 at 5:45 PM Andrew Jones <ajones@ventanamicro.com> wrote:
>
> On Wed, Nov 09, 2022 at 12:40:56AM -0500, guoren@kernel.org wrote:
> > From: Guo Ren <guoren@linux.alibaba.com>
> >
> > After use_asid_allocator is enabled, the userspace application will
> > crash by stale TLB entries. Because only using cpumask_clear_cpu without
> > local_flush_tlb_all couldn't guarantee CPU's TLB entries were fresh.
> > Then set_mm_asid would cause the user space application to get a stale
> > value by 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 /2x 0x3fd6d92490
> > 0x3fd6d92490:   0xd80ac8a8      0x0000003f
> > The core dump file shows that register s0 is wrong, but the value in
> > memory is correct. Because 'ld s0, -148(s0)' used a stale mapping entry
> > in TLB and got a wrong result from an incorrect physical address.
> >
> > When the task ran on CPU0, which loaded/speculative-loaded the value of
> > address(0x3fd6d92490), then the first version of the mapping entry was
> > PTWed into CPU0's TLB.
> > When the task switched from CPU0 to CPU1 (No local_tlb_flush_all here by
> > asid), it happened to write a value on the 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 the previous
> > switch_mm. So we only flushed the CPU1 TLB and set the second version
> > mapping of the PTE. When the task switched from CPU1 to CPU0 again, CPU0
> > still used a stale TLB mapping entry which contained a wrong target
> > physical address. It raised a bug when the task happened to read that
> > value.
> >
> > The solution is to keep all CPUs' footmarks of cpumask(mm) in switch_mm,
> > which could prevent losing pieces of stuff during TLB flush.
> >
> > Fixes: 65d4b9c53017 ("RISC-V: Implement ASID allocator")
> > Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
> > Signed-off-by: Guo Ren <guoren@kernel.org>
> > Cc: Anup Patel <apatel@ventanamicro.com>
> > Cc: Palmer Dabbelt <palmer@rivosinc.com>
> > ---
> > Changes in v2:
> >  - Fixup nommu compile problem (Thx Conor, Also Reported-by: kernel
> >    test robot <lkp@intel.com>)
> >  - Keep cpumask_clear_cpu for noasid
> > ---
> >  arch/riscv/mm/context.c | 6 +++++-
> >  1 file changed, 5 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/riscv/mm/context.c b/arch/riscv/mm/context.c
> > index 7acbfbd14557..f58e4b211595 100644
> > --- a/arch/riscv/mm/context.c
> > +++ b/arch/riscv/mm/context.c
> > @@ -317,7 +317,11 @@ void switch_mm(struct mm_struct *prev, struct mm_struct *next,
> >        */
> >       cpu = smp_processor_id();
> >
> > -     cpumask_clear_cpu(cpu, mm_cpumask(prev));
> > +#ifdef CONFIG_MMU
> > +     if (!static_branch_unlikely(&use_asid_allocator))
> > +#endif
>
> That's not very pretty. Can't we just do the following, instead?
>
> diff --git a/arch/riscv/mm/context.c b/arch/riscv/mm/context.c
> index 7acbfbd14557..ace419761e31 100644
> --- a/arch/riscv/mm/context.c
> +++ b/arch/riscv/mm/context.c
> @@ -16,10 +16,11 @@
>  #include <asm/cacheflush.h>
>  #include <asm/mmu_context.h>
>
> -#ifdef CONFIG_MMU
>
>  DEFINE_STATIC_KEY_FALSE(use_asid_allocator);
Define use_asid_allocator in nommu part? How about:

diff --git a/arch/riscv/mm/context.c b/arch/riscv/mm/context.c
index 7acbfbd14557..ed3f8de7ef97 100644
--- a/arch/riscv/mm/context.c
+++ b/arch/riscv/mm/context.c
@@ -205,12 +205,16 @@ static void set_mm_noasid(struct mm_struct *mm)
        local_flush_tlb_all();
 }

-static inline void set_mm(struct mm_struct *mm, unsigned int cpu)
+static inline void set_mm(struct mm_struct *prev,
+                         struct mm_struct *next, unsigned int cpu)
 {
-       if (static_branch_unlikely(&use_asid_allocator))
-               set_mm_asid(mm, cpu);
-       else
-               set_mm_noasid(mm);
+       cpumask_set_cpu(cpu, mm_cpumask(next));
+       if (static_branch_unlikely(&use_asid_allocator)) {
+               set_mm_asid(next, cpu);
+       } else {
+               cpumask_clear_cpu(cpu, mm_cpumask(prev));
+               set_mm_noasid(next);
+       }
 }

 static int __init asids_init(void)
@@ -264,7 +268,8 @@ static int __init asids_init(void)
 }
 early_initcall(asids_init);
 #else
-static inline void set_mm(struct mm_struct *mm, unsigned int cpu)
+static inline void set_mm(struct mm_struct *prev,
+                         struct mm_struct *next, unsigned int cpu)
 {
        /* Nothing to do here when there is no MMU */
 }
@@ -317,10 +322,7 @@ void switch_mm(struct mm_struct *prev, struct
mm_struct *next,
         */
        cpu = smp_processor_id();

-       cpumask_clear_cpu(cpu, mm_cpumask(prev));
-       cpumask_set_cpu(cpu, mm_cpumask(next));
-
-       set_mm(next, cpu);
+       set_mm(prev, next, cpu);

        flush_icache_deferred(next, cpu);

>
> +#ifdef CONFIG_MMU
> +
>  static unsigned long asid_bits;
>  static unsigned long num_asids;
>  static unsigned long asid_mask;
>
>
> Thanks,
> drew
>
> > +             cpumask_clear_cpu(cpu, mm_cpumask(prev));
> > +
> >       cpumask_set_cpu(cpu, mm_cpumask(next));
> >
> >       set_mm(next, cpu);
> > --
> > 2.36.1
> >
> >
> > _______________________________________________
> > linux-riscv mailing list
> > linux-riscv@lists.infradead.org
> > http://lists.infradead.org/mailman/listinfo/linux-riscv



-- 
Best Regards
 Guo Ren

Re: [PATCH V2] riscv: asid: Fixup stale TLB entry cause application crash

[Andrew Jones]

On Thu, Nov 10, 2022 at 09:51:03AM +0800, Guo Ren wrote:
> On Wed, Nov 9, 2022 at 5:45 PM Andrew Jones <ajones@ventanamicro.com> wrote:
> >
> > On Wed, Nov 09, 2022 at 12:40:56AM -0500, guoren@kernel.org wrote:
> > >
> > > -     cpumask_clear_cpu(cpu, mm_cpumask(prev));
> > > +#ifdef CONFIG_MMU
> > > +     if (!static_branch_unlikely(&use_asid_allocator))
> > > +#endif
> >
> > That's not very pretty. Can't we just do the following, instead?
> >
> > diff --git a/arch/riscv/mm/context.c b/arch/riscv/mm/context.c
> > index 7acbfbd14557..ace419761e31 100644
> > --- a/arch/riscv/mm/context.c
> > +++ b/arch/riscv/mm/context.c
> > @@ -16,10 +16,11 @@
> >  #include <asm/cacheflush.h>
> >  #include <asm/mmu_context.h>
> >
> > -#ifdef CONFIG_MMU
> >
> >  DEFINE_STATIC_KEY_FALSE(use_asid_allocator);
> Define use_asid_allocator in nommu part? How about:

Yeah, I was thinking it'll just always be a false static branch
in the nommu case, but I like your proposal below better.

Thanks,
drew

> 
> diff --git a/arch/riscv/mm/context.c b/arch/riscv/mm/context.c
> index 7acbfbd14557..ed3f8de7ef97 100644
> --- a/arch/riscv/mm/context.c
> +++ b/arch/riscv/mm/context.c
> @@ -205,12 +205,16 @@ static void set_mm_noasid(struct mm_struct *mm)
>         local_flush_tlb_all();
>  }
> 
> -static inline void set_mm(struct mm_struct *mm, unsigned int cpu)
> +static inline void set_mm(struct mm_struct *prev,
> +                         struct mm_struct *next, unsigned int cpu)
>  {
> -       if (static_branch_unlikely(&use_asid_allocator))
> -               set_mm_asid(mm, cpu);
> -       else
> -               set_mm_noasid(mm);
> +       cpumask_set_cpu(cpu, mm_cpumask(next));
> +       if (static_branch_unlikely(&use_asid_allocator)) {
> +               set_mm_asid(next, cpu);
> +       } else {
> +               cpumask_clear_cpu(cpu, mm_cpumask(prev));
> +               set_mm_noasid(next);
> +       }
>  }
> 
>  static int __init asids_init(void)
> @@ -264,7 +268,8 @@ static int __init asids_init(void)
>  }
>  early_initcall(asids_init);
>  #else
> -static inline void set_mm(struct mm_struct *mm, unsigned int cpu)
> +static inline void set_mm(struct mm_struct *prev,
> +                         struct mm_struct *next, unsigned int cpu)
>  {
>         /* Nothing to do here when there is no MMU */
>  }
> @@ -317,10 +322,7 @@ void switch_mm(struct mm_struct *prev, struct
> mm_struct *next,
>          */
>         cpu = smp_processor_id();
> 
> -       cpumask_clear_cpu(cpu, mm_cpumask(prev));
> -       cpumask_set_cpu(cpu, mm_cpumask(next));
> -
> -       set_mm(next, cpu);
> +       set_mm(prev, next, cpu);
> 
>         flush_icache_deferred(next, cpu);
> 
> >
> > +#ifdef CONFIG_MMU
> > +
> >  static unsigned long asid_bits;
> >  static unsigned long num_asids;
> >  static unsigned long asid_mask;
> >
> >
> > Thanks,
> > drew
> >
> > > +             cpumask_clear_cpu(cpu, mm_cpumask(prev));
> > > +
> > >       cpumask_set_cpu(cpu, mm_cpumask(next));
> > >
> > >       set_mm(next, cpu);
> > > --
> > > 2.36.1
> > >
> > >
> > > _______________________________________________
> > > linux-riscv mailing list
> > > linux-riscv@lists.infradead.org
> > > http://lists.infradead.org/mailman/listinfo/linux-riscv
> 
> 
> 
> -- 
> Best Regards
>  Guo Ren