Re: [PATCH v38 18/24] x86/vdso: Add support for exception fixup in vDSO functions

[Jarkko Sakkinen]

On Thu, Sep 24, 2020 at 12:07:12AM +0200, Borislav Petkov wrote:
> On Tue, Sep 15, 2020 at 02:28:36PM +0300, Jarkko Sakkinen wrote:
> > From: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
> > 
> > The basic concept and implementation is very similar to the kernel's
> > exception fixup mechanism.  The key differences are that the kernel
> > handler is hardcoded and the fixup entry addresses are relative to
> > the overall table as opposed to individual entries.
> 
> ...
> 
> This gist of this commit message should be also in
> Documentation/x86/sgx.rst
> 
> And I already said the same thing during v33 review:
> 
> "That is a very good explanation and I would prefer if it would be in a
> sgx-specific README or so instead of it getting lost in git..."
> 
> ...

This is not technically SGX specific patch. Is SGX documentation the
correct place for this?

> > diff --git a/arch/x86/entry/vdso/extable.h b/arch/x86/entry/vdso/extable.h
> > new file mode 100644
> > index 000000000000..aafdac396948
> > --- /dev/null
> > +++ b/arch/x86/entry/vdso/extable.h
> > @@ -0,0 +1,29 @@
> > +/* SPDX-License-Identifier: GPL-2.0 */
> > +#ifndef __VDSO_EXTABLE_H
> > +#define __VDSO_EXTABLE_H
> > +
> > +/*
> > + * Inject exception fixup for vDSO code.  Unlike normal exception fixup,
> > + * vDSO uses a dedicated handler the addresses are relative to the overall
> > + * exception table, not each individual entry.
> > + */
> > +#ifdef __ASSEMBLY__
> > +#define _ASM_VDSO_EXTABLE_HANDLE(from, to)	\
> > +	ASM_VDSO_EXTABLE_HANDLE from to
> > +
> > +.macro ASM_VDSO_EXTABLE_HANDLE from:req to:req
> > +	.pushsection __ex_table, "a"
> > +	.long (\from) - __ex_table
> > +	.long (\to) - __ex_table
> > +	.popsection
> > +.endm
> > +#else
> > +#define _ASM_VDSO_EXTABLE_HANDLE(from, to)	\
> > +	".pushsection __ex_table, \"a\"\n"      \
> > +	".long (" #from ") - __ex_table\n"      \
> > +	".long (" #to ") - __ex_table\n"        \
> > +	".popsection\n"
> > +#endif
> > +
> > +#endif /* __VDSO_EXTABLE_H */
> > +
> 
> Also from last time:
> 
> .git/rebase-apply/patch:122: new blank line at EOF.
> +

>From checkpatch I only get:

ERROR: Macros with complex values should be enclosed in parentheses
#193: FILE: arch/x86/entry/vdso/extable.h:11:
+#define _ASM_VDSO_EXTABLE_HANDLE(from, to)	\
+	ASM_VDSO_EXTABLE_HANDLE from to

ERROR: need consistent spacing around '*' (ctx:WxV)
#244: FILE: arch/x86/entry/vdso/vdso2c.h:8:
+static void BITSFUNC(copy)(FILE *outfile, const unsigned char *data, size_t len)
                                 ^

ERROR: need consistent spacing around '*' (ctx:WxV)
#263: FILE: arch/x86/entry/vdso/vdso2c.h:27:
+			      FILE *outfile, ELF(Shdr) *sec, const char *name)

I did fix it now. Thanks.

> -- 
> Regards/Gruss,
>     Boris.
> 
> https://people.kernel.org/tglx/notes-about-netiquette

/Jarkko