Re: [RFC PATCH -next V2 4/7] arm64: add copy_from_user to machine check safe

[Tong Tiangen]

在 2022/4/6 19:19, Mark Rutland 写道:
> On Wed, Apr 06, 2022 at 09:13:08AM +0000, Tong Tiangen wrote:
> > Add scenarios copy_from_user to machine check safe.
> >
> > The data copied is user data and is machine check safe, so just kill
> > the user process and isolate the error page, not necessary panic.
> >
> > Signed-off-by: Tong Tiangen <tongtiangen@xxxxxxxxxx>
> > ---
> >   arch/arm64/include/asm/asm-uaccess.h | 16 ++++++++++++++++
> >   arch/arm64/lib/copy_from_user.S      | 11 ++++++-----
> >   2 files changed, 22 insertions(+), 5 deletions(-)
> >
> > diff --git a/arch/arm64/include/asm/asm-uaccess.h b/arch/arm64/include/asm/asm-uaccess.h
> > index 0557af834e03..f31c8978e1af 100644
> > --- a/arch/arm64/include/asm/asm-uaccess.h
> > +++ b/arch/arm64/include/asm/asm-uaccess.h
> > @@ -92,4 +92,20 @@ alternative_else_nop_endif
> >   
> >   		_asm_extable	8888b,\l;
> >   	.endm
> > +
> > +	.macro user_ldp_mc l, reg1, reg2, addr, post_inc
> > +8888:		ldtr	\reg1, [\addr];
> > +8889:		ldtr	\reg2, [\addr, #8];
> > +		add	\addr, \addr, \post_inc;
> > +
> > +		_asm_extable_mc	8888b, \l;
> > +		_asm_extable_mc	8889b, \l;
> > +	.endm
> > +
> > +	.macro user_ldst_mc l, inst, reg, addr, post_inc
> > +8888:		\inst		\reg, [\addr];
> > +		add		\addr, \addr, \post_inc;
> > +
> > +		_asm_extable_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..d9d7c5291871 100644
> > --- a/arch/arm64/lib/copy_from_user.S
> > +++ b/arch/arm64/lib/copy_from_user.S
> > @@ -21,7 +21,7 @@
> >    */
> >   
> >   	.macro ldrb1 reg, ptr, val
> > -	user_ldst 9998f, ldtrb, \reg, \ptr, \val
> > +	user_ldst_mc 9998f, ldtrb, \reg, \ptr, \val
> >   	.endm
> >   
> >   	.macro strb1 reg, ptr, val
> > @@ -29,7 +29,7 @@
> >   	.endm
> >   
> >   	.macro ldrh1 reg, ptr, val
> > -	user_ldst 9997f, ldtrh, \reg, \ptr, \val
> > +	user_ldst_mc 9997f, ldtrh, \reg, \ptr, \val
> >   	.endm
> >   
> >   	.macro strh1 reg, ptr, val
> > @@ -37,7 +37,7 @@
> >   	.endm
> >   
> >   	.macro ldr1 reg, ptr, val
> > -	user_ldst 9997f, ldtr, \reg, \ptr, \val
> > +	user_ldst_mc 9997f, ldtr, \reg, \ptr, \val
> >   	.endm
> >   
> >   	.macro str1 reg, ptr, val
> > @@ -45,7 +45,7 @@
> >   	.endm
> >   
> >   	.macro ldp1 reg1, reg2, ptr, val
> > -	user_ldp 9997f, \reg1, \reg2, \ptr, \val
> > +	user_ldp_mc 9997f, \reg1, \reg2, \ptr, \val
> >   	.endm
> >   
> >   	.macro stp1 reg1, reg2, ptr, val
> > @@ -62,7 +62,8 @@ SYM_FUNC_START(__arch_copy_from_user)
> >   	ret
> >   
> >   	// Exception fixups
> > -9997:	cmp	dst, dstin
> > +9997:	cbz	x0, 9998f			// Check machine check exception
> > +	cmp	dst, dstin
> >   	b.ne	9998f
>
> If you look at the copy template, you'd see that `dstin` *is* x0.
>
> Consier if we took a non-SEA fault. The the fixup handler will overwrite x0,
> it's likely `dst` != `dstin`, and we'll branch to the byte-by-byte copy. Or if
> we're doing something odd and mmap_min_addr is 0, we can do the wrong thing the
> other way around and *not* branch to the byte-by-byte copy when we should.
>
> So this is at best confusing, but likely broken too.
>
> Thanks,
> Mark.

OK, missing that, will be fixed in next verison.

Thanks,
Tong.

> >   	// Before being absolutely sure we couldn't copy anything, try harder
> >   USER(9998f, ldtrb tmp1w, [srcin])
> > --
> > 2.18.0.huawei.25
> >
> >
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> .