Re: [PATCH -next v5 2/8] arm64: extable: make uaaccess helper use extable type EX_TYPE_UACCESS_ERR_ZERO

[Tong Tiangen]

在 2022/6/18 11:26, Tong Tiangen 写道:
> 在 2022/6/17 16:24, Mark Rutland 写道:
> > On Sat, May 28, 2022 at 06:50:50AM +0000, Tong Tiangen wrote:
> > > Currnetly, the extable type used by __arch_copy_from/to_user() is
> > > EX_TYPE_FIXUP. In fact, It is more clearly to use meaningful
> > > EX_TYPE_UACCESS_*.
> > >
> > > Suggested-by: Mark Rutland <mark.rutland@xxxxxxx>
> > > Signed-off-by: Tong Tiangen <tongtiangen@xxxxxxxxxx>
> > > ---
> > >   arch/arm64/include/asm/asm-extable.h |  8 ++++++++
> > >   arch/arm64/include/asm/asm-uaccess.h | 12 ++++++------
> > >   2 files changed, 14 insertions(+), 6 deletions(-)
> > >
> > > diff --git a/arch/arm64/include/asm/asm-extable.h 
> > > b/arch/arm64/include/asm/asm-extable.h
> > > index 56ebe183e78b..9c94ac1f082c 100644
> > > --- a/arch/arm64/include/asm/asm-extable.h
> > > +++ b/arch/arm64/include/asm/asm-extable.h
> > > @@ -28,6 +28,14 @@
> > >       __ASM_EXTABLE_RAW(\insn, \fixup, EX_TYPE_FIXUP, 0)
> > >       .endm
> > > +/*
> > > + * Create an exception table entry for uaccess `insn`, which will 
> > > branch to `fixup`
> > > + * when an unhandled fault is taken.
> > > + * ex->data = ~0 means both reg_err and reg_zero is set to wzr(x31).
> > > + */
> > > +    .macro          _asm_extable_uaccess, insn, fixup
> > > +    __ASM_EXTABLE_RAW(\insn, \fixup, EX_TYPE_UACCESS_ERR_ZERO, ~0)
> > > +    .endm
> >
> > I'm not too keen on using `~0` here, since that also sets other bits 
> > in the
> > data field, and its somewhat opaque.
> >
> > How painful is it to generate the data fields as with the C version of 
> > this
> > macro, so that we can pass in wzr explciitly for the two sub-fields?
> >
> > Other than that, this looks good to me.
> >
> > Thanks,
> > Mark.
>
> ok, will fix next version.
>
> Thanks,
> Tong.

I tried to using data filelds as with C version, but here assembly code 
we can not using operator such as << and |, if we use lsl and orr 
instructions, the gpr will be occupied.

So how about using 0x3ff directly here? it means err register and zero 
register both set to x31.

Thanks,
Tong.

> > >   /*
> > >    * 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..75b211c98dea 100644
> > > --- a/arch/arm64/include/asm/asm-uaccess.h
> > > +++ b/arch/arm64/include/asm/asm-uaccess.h
> > > @@ -61,7 +61,7 @@ alternative_else_nop_endif
> > >   #define USER(l, x...)                \
> > >   9999:    x;                    \
> > > -    _asm_extable    9999b, l
> > > +    _asm_extable_uaccess    9999b, l
> > >   /*
> > >    * Generate the assembly for LDTR/STTR with exception table entries.
> > > @@ -73,8 +73,8 @@ 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    8888b, \l;
> > > +        _asm_extable_uaccess    8889b, \l;
> > >       .endm
> > >       .macro user_stp l, reg1, reg2, addr, post_inc
> > > @@ -82,14 +82,14 @@ 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    8888b,\l;
> > > +        _asm_extable_uaccess    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    8888b, \l;
> > >       .endm
> > >   #endif
> > > --
> > > 2.25.1
> > .
>
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