On Wed, Apr 20, 2022 at 03:04:15AM +, Tong Tiangen wrote:
> Add copy_{to, from}_user() to machine check safe.
>
> If copy fail due to hardware memory error, only the relevant processes are
> affected, so killing the user process and isolate the user page with
> hardware memory errors is a more reasonable choice than kernel panic.
>
> Add new extable type EX_TYPE_UACCESS_MC which can be used for uaccess that
> can be recovered from hardware memory errors.
I don't understand why we need this.
If we apply EX_TYPE_UACCESS consistently to *all* user accesses, and
*only* to user accesses, that would *always* indicate that we can
recover, and that seems much simpler to deal with.
Today we use EX_TYPE_UACCESS_ERR_ZERO for kernel accesses in a couple of
cases, which we should clean up, and we user EX_TYPE_FIXUP for a couple
of user accesses, but those could easily be converted over.
> The x16 register is used to save the fixup type in copy_xxx_user which
> used extable type EX_TYPE_UACCESS_MC.
Why x16?
How is this intended to be consumed, and why is that behaviour different
from any *other* fault?
Mark.
> Signed-off-by: Tong Tiangen
> ---
> arch/arm64/include/asm/asm-extable.h | 14 ++
> arch/arm64/include/asm/asm-uaccess.h | 15 ++-
> arch/arm64/lib/copy_from_user.S | 18 +++---
> arch/arm64/lib/copy_to_user.S| 18 +++---
> arch/arm64/mm/extable.c | 18 ++
> 5 files changed, 60 insertions(+), 23 deletions(-)
>
> diff --git a/arch/arm64/include/asm/asm-extable.h
> b/arch/arm64/include/asm/asm-extable.h
> index c39f2437e08e..75b2c00e9523 100644
> --- a/arch/arm64/include/asm/asm-extable.h
> +++ b/arch/arm64/include/asm/asm-extable.h
> @@ -2,12 +2,18 @@
> #ifndef __ASM_ASM_EXTABLE_H
> #define __ASM_ASM_EXTABLE_H
>
> +#define FIXUP_TYPE_NORMAL0
> +#define FIXUP_TYPE_MC1
> +
> #define EX_TYPE_NONE 0
> #define EX_TYPE_FIXUP1
> #define EX_TYPE_BPF 2
> #define EX_TYPE_UACCESS_ERR_ZERO 3
> #define EX_TYPE_LOAD_UNALIGNED_ZEROPAD 4
>
> +/* _MC indicates that can fixup from machine check errors */
> +#define EX_TYPE_UACCESS_MC 5
> +
> #ifdef __ASSEMBLY__
>
> #define __ASM_EXTABLE_RAW(insn, fixup, type, data) \
> @@ -27,6 +33,14 @@
> __ASM_EXTABLE_RAW(\insn, \fixup, EX_TYPE_FIXUP, 0)
> .endm
>
> +/*
> + * Create an exception table entry for `insn`, which will branch to `fixup`
> + * when an unhandled fault(include sea fault) is taken.
> + */
> + .macro _asm_extable_uaccess_mc, insn, fixup
> + __ASM_EXTABLE_RAW(\insn, \fixup, EX_TYPE_UACCESS_MC, 0)
> + .endm
> +
> /*
> * Create an exception table entry for `insn` if `fixup` is provided.
> Otherwise
> * do nothing.
> diff --git a/arch/arm64/include/asm/asm-uaccess.h
> b/arch/arm64/include/asm/asm-uaccess.h
> index 0557af834e03..6c23c138e1fc 100644
> --- a/arch/arm64/include/asm/asm-uaccess.h
> +++ b/arch/arm64/include/asm/asm-uaccess.h
> @@ -63,6 +63,11 @@ alternative_else_nop_endif
> :x; \
> _asm_extableb, l
>
> +
> +#define USER_MC(l, x...) \
> +:x; \
> + _asm_extable_uaccess_mc b, l
> +
> /*
> * Generate the assembly for LDTR/STTR with exception table entries.
> * This is complicated as there is no post-increment or pair versions of the
> @@ -73,8 +78,8 @@ alternative_else_nop_endif
> 8889:ldtr\reg2, [\addr, #8];
> add \addr, \addr, \post_inc;
>
> - _asm_extableb,\l;
> - _asm_extable8889b,\l;
> + _asm_extable_uaccess_mc b, \l;
> + _asm_extable_uaccess_mc 8889b, \l;
> .endm
>
> .macro user_stp l, reg1, reg2, addr, post_inc
> @@ -82,14 +87,14 @@ alternative_else_nop_endif
> 8889:sttr\reg2, [\addr, #8];
> add \addr, \addr, \post_inc;
>
> - _asm_extableb,\l;
> - _asm_extable8889b,\l;
> + _asm_extable_uaccess_mc b,\l;
> + _asm_extable_uaccess_mc 8889b,\l;
> .endm
>
> .macro user_ldst l, inst, reg, addr, post_inc
> :\inst \reg, [\addr];
> add \addr, \addr, \post_inc;
>
> - _asm_extableb,\l;
> + _asm_extable_uaccess_mc b, \l;
> .endm
> #endif
> diff --git a/arch/arm64/lib/copy_from_user.S b/arch/arm64/lib/copy_from_user.S
> index 34e317907524..480cc5ac0a8d 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_MC(9998f, strb \reg, [\ptr], \val)
> .endm
>
> .macro
