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

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Date:   Thu, 24 Sep 2020 15:09:01 +0300
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     x86@...nel.org, linux-sgx@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Andy Lutomirski <luto@...capital.net>,
        Jethro Beekman <jethro@...tanix.com>,
        akpm@...ux-foundation.org, andriy.shevchenko@...ux.intel.com,
        asapek@...gle.com, cedric.xing@...el.com, chenalexchen@...gle.com,
        conradparker@...gle.com, cyhanish@...gle.com,
        dave.hansen@...el.com, haitao.huang@...el.com,
        josh@...htriplett.org, kai.huang@...el.com, kai.svahn@...el.com,
        kmoy@...gle.com, ludloff@...gle.com, luto@...nel.org,
        nhorman@...hat.com, npmccallum@...hat.com, puiterwijk@...hat.com,
        rientjes@...gle.com, tglx@...utronix.de, yaozhangx@...gle.com
Subject: Re: [PATCH v38 18/24] x86/vdso: Add support for exception fixup in
 vDSO functions

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@...el.com>
> > 
> > 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