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Message-ID: <Yn55uz52Hn3gF9Xe@lakrids>
Date: Fri, 13 May 2022 16:31:07 +0100
From: Mark Rutland <mark.rutland@....com>
To: Tong Tiangen <tongtiangen@...wei.com>
Cc: James Morse <james.morse@....com>,
Andrew Morton <akpm@...ux-foundation.org>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
Robin Murphy <robin.murphy@....com>,
Dave Hansen <dave.hansen@...ux.intel.com>,
Catalin Marinas <catalin.marinas@....com>,
Will Deacon <will@...nel.org>,
Alexander Viro <viro@...iv.linux.org.uk>,
Michael Ellerman <mpe@...erman.id.au>,
Benjamin Herrenschmidt <benh@...nel.crashing.org>,
Paul Mackerras <paulus@...ba.org>, x86@...nel.org,
"H . Peter Anvin" <hpa@...or.com>, linuxppc-dev@...ts.ozlabs.org,
linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
linux-mm@...ck.org, Kefeng Wang <wangkefeng.wang@...wei.com>,
Xie XiuQi <xiexiuqi@...wei.com>,
Guohanjun <guohanjun@...wei.com>
Subject: Re: [PATCH -next v4 4/7] arm64: add copy_{to, from}_user to machine
check safe
On Wed, Apr 20, 2022 at 03:04:15AM +0000, 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 <tongtiangen@...wei.com>
> ---
> 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_NORMAL 0
> +#define FIXUP_TYPE_MC 1
> +
> #define EX_TYPE_NONE 0
> #define EX_TYPE_FIXUP 1
> #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
> 9999: x; \
> _asm_extable 9999b, l
>
> +
> +#define USER_MC(l, x...) \
> +9999: x; \
> + _asm_extable_uaccess_mc 9999b, 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_extable 8888b,\l;
> - _asm_extable 8889b,\l;
> + _asm_extable_uaccess_mc 8888b, \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_extable 8888b,\l;
> - _asm_extable 8889b,\l;
> + _asm_extable_uaccess_mc 8888b,\l;
> + _asm_extable_uaccess_mc 8889b,\l;
> .endm
>
> .macro user_ldst l, inst, reg, addr, post_inc
> 8888: \inst \reg, [\addr];
> add \addr, \addr, \post_inc;
>
> - _asm_extable 8888b,\l;
> + _asm_extable_uaccess_mc 8888b, \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 ldrh1 reg, ptr, val
> @@ -33,7 +33,7 @@
> .endm
>
> .macro strh1 reg, ptr, val
> - strh \reg, [\ptr], \val
> + USER_MC(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_MC(9998f, str \reg, [\ptr], \val)
> .endm
>
> .macro ldp1 reg1, reg2, ptr, val
> @@ -49,11 +49,12 @@
> .endm
>
> .macro stp1 reg1, reg2, ptr, val
> - stp \reg1, \reg2, [\ptr], \val
> + USER_MC(9998f, stp \reg1, \reg2, [\ptr], \val)
> .endm
>
> -end .req x5
> -srcin .req x15
> +end .req x5
> +srcin .req x15
> +fixup_type .req x16
> SYM_FUNC_START(__arch_copy_from_user)
> add end, x0, x2
> mov srcin, x1
> @@ -62,7 +63,10 @@ SYM_FUNC_START(__arch_copy_from_user)
> ret
>
> // Exception fixups
> -9997: cmp dst, dstin
> + // x16: fixup type written by ex_handler_uaccess_mc
> +9997: cmp fixup_type, #FIXUP_TYPE_MC
> + b.eq 9998f
> + cmp dst, dstin
> b.ne 9998f
> // Before being absolutely sure we couldn't copy anything, try harder
> USER(9998f, ldtrb tmp1w, [srcin])
> diff --git a/arch/arm64/lib/copy_to_user.S b/arch/arm64/lib/copy_to_user.S
> index 802231772608..021a7d27b3a4 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_MC(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_MC(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_MC(9998f, ldr \reg, [\ptr], \val)
> .endm
>
> .macro str1 reg, ptr, val
> @@ -44,15 +44,16 @@
> .endm
>
> .macro ldp1 reg1, reg2, ptr, val
> - ldp \reg1, \reg2, [\ptr], \val
> + USER_MC(9998f, ldp \reg1, \reg2, [\ptr], \val)
> .endm
>
> .macro stp1 reg1, reg2, ptr, val
> user_stp 9997f, \reg1, \reg2, \ptr, \val
> .endm
>
> -end .req x5
> -srcin .req x15
> +end .req x5
> +srcin .req x15
> +fixup_type .req x16
> SYM_FUNC_START(__arch_copy_to_user)
> add end, x0, x2
> mov srcin, x1
> @@ -61,7 +62,10 @@ SYM_FUNC_START(__arch_copy_to_user)
> ret
>
> // Exception fixups
> -9997: cmp dst, dstin
> + // x16: fixup type written by ex_handler_uaccess_mc
> +9997: cmp fixup_type, #FIXUP_TYPE_MC
> + b.eq 9998f
> + cmp dst, dstin
> b.ne 9998f
> // Before being absolutely sure we couldn't copy anything, try harder
> ldrb tmp1w, [srcin]
> diff --git a/arch/arm64/mm/extable.c b/arch/arm64/mm/extable.c
> index 4f0083a550d4..525876c3ebf4 100644
> --- a/arch/arm64/mm/extable.c
> +++ b/arch/arm64/mm/extable.c
> @@ -24,6 +24,14 @@ static bool ex_handler_fixup(const struct exception_table_entry *ex,
> return true;
> }
>
> +static bool ex_handler_uaccess_type(const struct exception_table_entry *ex,
> + struct pt_regs *regs,
> + unsigned long fixup_type)
> +{
> + regs->regs[16] = fixup_type;
> + return ex_handler_fixup(ex, regs);
> +}
> +
> static bool ex_handler_uaccess_err_zero(const struct exception_table_entry *ex,
> struct pt_regs *regs)
> {
> @@ -75,6 +83,8 @@ bool fixup_exception(struct pt_regs *regs)
> switch (ex->type) {
> case EX_TYPE_FIXUP:
> return ex_handler_fixup(ex, regs);
> + case EX_TYPE_UACCESS_MC:
> + return ex_handler_uaccess_type(ex, regs, FIXUP_TYPE_NORMAL);
> case EX_TYPE_BPF:
> return ex_handler_bpf(ex, regs);
> case EX_TYPE_UACCESS_ERR_ZERO:
> @@ -94,10 +104,10 @@ 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_MC:
> + return ex_handler_uaccess_type(ex, regs, FIXUP_TYPE_MC);
> + }
>
> return false;
> }
> --
> 2.25.1
>
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