On Sat, May 28, 2022 at 06:50:55AM +0000, Tong Tiangen wrote:
> If user access fail due to hardware memory error, only the relevant
> processes are affected, so killing the user process and isolate the
> error page with hardware memory errors is a more reasonable choice
> than kernel panic.
>
> Signed-off-by: Tong Tiangen <[email protected]>
> ---
> arch/arm64/lib/copy_from_user.S | 8 ++++----
> arch/arm64/lib/copy_to_user.S | 8 ++++----
All of these changes are to the *kernel* accesses performed as part of copy
to/from user, and have nothing to do with userspace, so it does not make sense
to mark these as UACCESS.
Do we *actually* need to recover from failues on these accesses? Looking at
_copy_from_user(), the kernel will immediately follow this up with a memset()
to the same address which will be fatal anyway, so this is only punting the
failure for a few instructions.
If we really need to recover from certain accesses to kernel memory we should
add a new EX_TYPE_KACCESS_ERR_ZERO_MC or similar, but we need a strong
rationale as to why that's useful. As things stand I do not beleive it makes
sense for copy to/from user specifically.
> arch/arm64/mm/extable.c | 8 ++++----
> 3 files changed, 12 insertions(+), 12 deletions(-)
>
> diff --git a/arch/arm64/lib/copy_from_user.S b/arch/arm64/lib/copy_from_user.S
> index 34e317907524..402dd48a4f93 100644
> --- a/arch/arm64/lib/copy_from_user.S
> +++ b/arch/arm64/lib/copy_from_user.S
> @@ -25,7 +25,7 @@
> .endm
>
> .macro strb1 reg, ptr, val
> - strb \reg, [\ptr], \val
> + USER(9998f, strb \reg, [\ptr], \val)
> .endm
>
> .macro ldrh1 reg, ptr, val
> @@ -33,7 +33,7 @@
> .endm
>
> .macro strh1 reg, ptr, val
> - strh \reg, [\ptr], \val
> + USER(9998f, strh \reg, [\ptr], \val)
> .endm
>
> .macro ldr1 reg, ptr, val
> @@ -41,7 +41,7 @@
> .endm
>
> .macro str1 reg, ptr, val
> - str \reg, [\ptr], \val
> + USER(9998f, str \reg, [\ptr], \val)
> .endm
>
> .macro ldp1 reg1, reg2, ptr, val
> @@ -49,7 +49,7 @@
> .endm
>
> .macro stp1 reg1, reg2, ptr, val
> - stp \reg1, \reg2, [\ptr], \val
> + USER(9998f, stp \reg1, \reg2, [\ptr], \val)
> .endm
>
> end .req x5
> diff --git a/arch/arm64/lib/copy_to_user.S b/arch/arm64/lib/copy_to_user.S
> index 802231772608..4134bdb3a8b0 100644
> --- a/arch/arm64/lib/copy_to_user.S
> +++ b/arch/arm64/lib/copy_to_user.S
> @@ -20,7 +20,7 @@
> * x0 - bytes not copied
> */
> .macro ldrb1 reg, ptr, val
> - ldrb \reg, [\ptr], \val
> + USER(9998f, ldrb \reg, [\ptr], \val)
> .endm
>
> .macro strb1 reg, ptr, val
> @@ -28,7 +28,7 @@
> .endm
>
> .macro ldrh1 reg, ptr, val
> - ldrh \reg, [\ptr], \val
> + USER(9998f, ldrh \reg, [\ptr], \val)
> .endm
>
> .macro strh1 reg, ptr, val
> @@ -36,7 +36,7 @@
> .endm
>
> .macro ldr1 reg, ptr, val
> - ldr \reg, [\ptr], \val
> + USER(9998f, ldr \reg, [\ptr], \val)
> .endm
>
> .macro str1 reg, ptr, val
> @@ -44,7 +44,7 @@
> .endm
>
> .macro ldp1 reg1, reg2, ptr, val
> - ldp \reg1, \reg2, [\ptr], \val
> + USER(9998f, ldp \reg1, \reg2, [\ptr], \val)
> .endm
>
> .macro stp1 reg1, reg2, ptr, val
> diff --git a/arch/arm64/mm/extable.c b/arch/arm64/mm/extable.c
> index c301dcf6335f..8ca8d9639f9f 100644
> --- a/arch/arm64/mm/extable.c
> +++ b/arch/arm64/mm/extable.c
> @@ -86,10 +86,10 @@ bool fixup_exception_mc(struct pt_regs *regs)
> if (!ex)
> return false;
>
> - /*
> - * This is not complete, More Machine check safe extable type can
> - * be processed here.
> - */
> + switch (ex->type) {
> + case EX_TYPE_UACCESS_ERR_ZERO:
> + return ex_handler_uaccess_err_zero(ex, regs);
> + }
This addition specifically makes sense to me, so can you split this into a separate patch?
Thanks,
Mark.
在 2022/6/17 17:06, Mark Rutland 写道:
> On Sat, May 28, 2022 at 06:50:55AM +0000, Tong Tiangen wrote:
>> If user access fail due to hardware memory error, only the relevant
>> processes are affected, so killing the user process and isolate the
>> error page with hardware memory errors is a more reasonable choice
>> than kernel panic.
>>
>> Signed-off-by: Tong Tiangen <[email protected]>
>
>> ---
>> arch/arm64/lib/copy_from_user.S | 8 ++++----
>> arch/arm64/lib/copy_to_user.S | 8 ++++----
>
> All of these changes are to the *kernel* accesses performed as part of copy
> to/from user, and have nothing to do with userspace, so it does not make sense
> to mark these as UACCESS.
You have a point. so there is no need to modify copy_from/to_user.S in
this patch set.
>
> Do we *actually* need to recover from failues on these accesses? Looking at
> _copy_from_user(), the kernel will immediately follow this up with a memset()
> to the same address which will be fatal anyway, so this is only punting the
> failure for a few instructions.
If recovery success, The task will be killed and there will be no
subsequent memset().
>
> If we really need to recover from certain accesses to kernel memory we should
> add a new EX_TYPE_KACCESS_ERR_ZERO_MC or similar, but we need a strong
> rationale as to why that's useful. As things stand I do not beleive it makes
> sense for copy to/from user specifically.
>
>> arch/arm64/mm/extable.c | 8 ++++----
>> 3 files changed, 12 insertions(+), 12 deletions(-)
>>
>> diff --git a/arch/arm64/lib/copy_from_user.S b/arch/arm64/lib/copy_from_user.S
>> index 34e317907524..402dd48a4f93 100644
>> --- a/arch/arm64/lib/copy_from_user.S
>> +++ b/arch/arm64/lib/copy_from_user.S
>> @@ -25,7 +25,7 @@
>> .endm
>>
>> .macro strb1 reg, ptr, val
>> - strb \reg, [\ptr], \val
>> + USER(9998f, strb \reg, [\ptr], \val)
>> .endm
>>
>> .macro ldrh1 reg, ptr, val
>> @@ -33,7 +33,7 @@
>> .endm
>>
>> .macro strh1 reg, ptr, val
>> - strh \reg, [\ptr], \val
>> + USER(9998f, strh \reg, [\ptr], \val)
>> .endm
>>
>> .macro ldr1 reg, ptr, val
>> @@ -41,7 +41,7 @@
>> .endm
>>
>> .macro str1 reg, ptr, val
>> - str \reg, [\ptr], \val
>> + USER(9998f, str \reg, [\ptr], \val)
>> .endm
>>
>> .macro ldp1 reg1, reg2, ptr, val
>> @@ -49,7 +49,7 @@
>> .endm
>>
>> .macro stp1 reg1, reg2, ptr, val
>> - stp \reg1, \reg2, [\ptr], \val
>> + USER(9998f, stp \reg1, \reg2, [\ptr], \val)
>> .endm
>>
>> end .req x5
>> diff --git a/arch/arm64/lib/copy_to_user.S b/arch/arm64/lib/copy_to_user.S
>> index 802231772608..4134bdb3a8b0 100644
>> --- a/arch/arm64/lib/copy_to_user.S
>> +++ b/arch/arm64/lib/copy_to_user.S
>> @@ -20,7 +20,7 @@
>> * x0 - bytes not copied
>> */
>> .macro ldrb1 reg, ptr, val
>> - ldrb \reg, [\ptr], \val
>> + USER(9998f, ldrb \reg, [\ptr], \val)
>> .endm
>>
>> .macro strb1 reg, ptr, val
>> @@ -28,7 +28,7 @@
>> .endm
>>
>> .macro ldrh1 reg, ptr, val
>> - ldrh \reg, [\ptr], \val
>> + USER(9998f, ldrh \reg, [\ptr], \val)
>> .endm
>>
>> .macro strh1 reg, ptr, val
>> @@ -36,7 +36,7 @@
>> .endm
>>
>> .macro ldr1 reg, ptr, val
>> - ldr \reg, [\ptr], \val
>> + USER(9998f, ldr \reg, [\ptr], \val)
>> .endm
>>
>> .macro str1 reg, ptr, val
>> @@ -44,7 +44,7 @@
>> .endm
>>
>> .macro ldp1 reg1, reg2, ptr, val
>> - ldp \reg1, \reg2, [\ptr], \val
>> + USER(9998f, ldp \reg1, \reg2, [\ptr], \val)
>> .endm
>>
>> .macro stp1 reg1, reg2, ptr, val
>> diff --git a/arch/arm64/mm/extable.c b/arch/arm64/mm/extable.c
>> index c301dcf6335f..8ca8d9639f9f 100644
>> --- a/arch/arm64/mm/extable.c
>> +++ b/arch/arm64/mm/extable.c
>> @@ -86,10 +86,10 @@ bool fixup_exception_mc(struct pt_regs *regs)
>> if (!ex)
>> return false;
>>
>> - /*
>> - * This is not complete, More Machine check safe extable type can
>> - * be processed here.
>> - */
>> + switch (ex->type) {
>> + case EX_TYPE_UACCESS_ERR_ZERO:
>> + return ex_handler_uaccess_err_zero(ex, regs);
>> + }
>
> This addition specifically makes sense to me, so can you split this into a separate patch?
According to my understanding of the above, only the modification of
extable.c is retained.
So what do you mean which part is made into a separate patch?
Thanks,
Tong.
>
> Thanks,
> Mark.
>
> .
On Sat, Jun 18, 2022 at 05:27:45PM +0800, Tong Tiangen wrote:
>
>
> 在 2022/6/17 17:06, Mark Rutland 写道:
> > On Sat, May 28, 2022 at 06:50:55AM +0000, Tong Tiangen wrote:
> > > If user access fail due to hardware memory error, only the relevant
> > > processes are affected, so killing the user process and isolate the
> > > error page with hardware memory errors is a more reasonable choice
> > > than kernel panic.
> > >
> > > Signed-off-by: Tong Tiangen <[email protected]>
> >
> > > ---
> > > arch/arm64/lib/copy_from_user.S | 8 ++++----
> > > arch/arm64/lib/copy_to_user.S | 8 ++++----
> >
> > All of these changes are to the *kernel* accesses performed as part of copy
> > to/from user, and have nothing to do with userspace, so it does not make sense
> > to mark these as UACCESS.
>
> You have a point. so there is no need to modify copy_from/to_user.S in this
> patch set.
Cool, thanks. If this patch just has the extable change, that's fine by me.
> > Do we *actually* need to recover from failues on these accesses? Looking at
> > _copy_from_user(), the kernel will immediately follow this up with a memset()
> > to the same address which will be fatal anyway, so this is only punting the
> > failure for a few instructions.
>
> If recovery success, The task will be killed and there will be no subsequent
> memset().
I don't think that's true.
IIUC per the last patch, in the exception handler we'll apply the fixup then
force a signal. That doesn't kill the task immediately, and we'll return from
the exception handler back into the original context (with the fixup applied).
The structure of copy_from_user() is
copy_from_user(to, from, n) {
_copy_from_user(to, from, n) {
res = n;
res = raw_copy_from_user(to, from, n);
if (res)
memset(to + (n - res), 0, res);
}
}
So when the fixup is applied and res indicates that the copy terminated early,
there is an unconditinal memset() before the fatal signal is handled in the
return to userspace path.
> > If we really need to recover from certain accesses to kernel memory we should
> > add a new EX_TYPE_KACCESS_ERR_ZERO_MC or similar, but we need a strong
> > rationale as to why that's useful. As things stand I do not beleive it makes
> > sense for copy to/from user specifically.
[...]
> > > diff --git a/arch/arm64/mm/extable.c b/arch/arm64/mm/extable.c
> > > index c301dcf6335f..8ca8d9639f9f 100644
> > > --- a/arch/arm64/mm/extable.c
> > > +++ b/arch/arm64/mm/extable.c
> > > @@ -86,10 +86,10 @@ bool fixup_exception_mc(struct pt_regs *regs)
> > > if (!ex)
> > > return false;
> > > - /*
> > > - * This is not complete, More Machine check safe extable type can
> > > - * be processed here.
> > > - */
> > > + switch (ex->type) {
> > > + case EX_TYPE_UACCESS_ERR_ZERO:
> > > + return ex_handler_uaccess_err_zero(ex, regs);
> > > + }
> >
> > This addition specifically makes sense to me, so can you split this into a separate patch?
>
> According to my understanding of the above, only the modification of
> extable.c is retained.
>
> So what do you mean which part is made into a separate patch?
As above, if you just retain the extable.c changes, that's fine by me.
Thanks,
Mark.
在 2022/6/18 19:35, Mark Rutland 写道:
> On Sat, Jun 18, 2022 at 05:27:45PM +0800, Tong Tiangen wrote:
>>
>>
>> 在 2022/6/17 17:06, Mark Rutland 写道:
>>> On Sat, May 28, 2022 at 06:50:55AM +0000, Tong Tiangen wrote:
>>>> If user access fail due to hardware memory error, only the relevant
>>>> processes are affected, so killing the user process and isolate the
>>>> error page with hardware memory errors is a more reasonable choice
>>>> than kernel panic.
>>>>
>>>> Signed-off-by: Tong Tiangen <[email protected]>
>>>
>>>> ---
>>>> arch/arm64/lib/copy_from_user.S | 8 ++++----
>>>> arch/arm64/lib/copy_to_user.S | 8 ++++----
>>>
>>> All of these changes are to the *kernel* accesses performed as part of copy
>>> to/from user, and have nothing to do with userspace, so it does not make sense
>>> to mark these as UACCESS.
>>
>> You have a point. so there is no need to modify copy_from/to_user.S in this
>> patch set.
>
> Cool, thanks. If this patch just has the extable change, that's fine by me.
>
>>> Do we *actually* need to recover from failues on these accesses? Looking at
>>> _copy_from_user(), the kernel will immediately follow this up with a memset()
>>> to the same address which will be fatal anyway, so this is only punting the
>>> failure for a few instructions.
>>
>> If recovery success, The task will be killed and there will be no subsequent
>> memset().
>
> I don't think that's true.
>
> IIUC per the last patch, in the exception handler we'll apply the fixup then
> force a signal. That doesn't kill the task immediately, and we'll return from
> the exception handler back into the original context (with the fixup applied).
>
correct.
> The structure of copy_from_user() is
>
> copy_from_user(to, from, n) {
> _copy_from_user(to, from, n) {
> res = n;
> res = raw_copy_from_user(to, from, n);
> if (res)
> memset(to + (n - res), 0, res);
> }
> }
>
> So when the fixup is applied and res indicates that the copy terminated early,
> there is an unconditinal memset() before the fatal signal is handled in the
> return to userspace path.
correct in this scenario.
My idea is also valuable in many other scenarios.
>
>>> If we really need to recover from certain accesses to kernel memory we should
>>> add a new EX_TYPE_KACCESS_ERR_ZERO_MC or similar, but we need a strong
>>> rationale as to why that's useful. As things stand I do not beleive it makes
>>> sense for copy to/from user specifically.
>
> [...]
>
>>>> diff --git a/arch/arm64/mm/extable.c b/arch/arm64/mm/extable.c
>>>> index c301dcf6335f..8ca8d9639f9f 100644
>>>> --- a/arch/arm64/mm/extable.c
>>>> +++ b/arch/arm64/mm/extable.c
>>>> @@ -86,10 +86,10 @@ bool fixup_exception_mc(struct pt_regs *regs)
>>>> if (!ex)
>>>> return false;
>>>> - /*
>>>> - * This is not complete, More Machine check safe extable type can
>>>> - * be processed here.
>>>> - */
>>>> + switch (ex->type) {
>>>> + case EX_TYPE_UACCESS_ERR_ZERO:
>>>> + return ex_handler_uaccess_err_zero(ex, regs);
>>>> + }
>>>
>>> This addition specifically makes sense to me, so can you split this into a separate patch?
>>
>> According to my understanding of the above, only the modification of
>> extable.c is retained.
>>
>> So what do you mean which part is made into a separate patch?
>
> As above, if you just retain the extable.c changes, that's fine by me.
Thanks,
Tong.
>
> Thanks,
> Mark.
> .