[PATCH] x86/mm/encrypt: Use %a asm operand modifier to obtain %rip-relative address

[PATCH] x86/mm/encrypt: Use %a asm operand modifier to obtain %rip-relative address

[Uros Bizjak]

The "a" asm operand modifier substitutes a memory reference, with the
actual operand treated as address.  For x86_64, when a symbol is
provided, the "a" modifier emits "sym(%rip)" instead of "sym".

Clang allows only "i" and "r" operand constraints with an "a" modifier,
so the patch normalizes the modifier/constraint pair to "a"/"i"
which is consistent between both compilers.

No functional change intended.

Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
---
 arch/x86/mm/mem_encrypt_identity.c | 16 ++++------------
 1 file changed, 4 insertions(+), 12 deletions(-)

diff --git a/arch/x86/mm/mem_encrypt_identity.c b/arch/x86/mm/mem_encrypt_identity.c
index d73aeb16417f..6a351fdd1b39 100644
--- a/arch/x86/mm/mem_encrypt_identity.c
+++ b/arch/x86/mm/mem_encrypt_identity.c
@@ -346,9 +346,7 @@ void __init sme_encrypt_kernel(struct boot_params *bp)
 	 * We're running identity mapped, so we must obtain the address to the
 	 * SME encryption workarea using rip-relative addressing.
 	 */
-	asm ("lea sme_workarea(%%rip), %0"
-	     : "=r" (workarea_start)
-	     : "p" (sme_workarea));
+	asm ("lea %a1, %0" : "=r" (workarea_start) : "i" (sme_workarea));
 
 	/*
 	 * Calculate required number of workarea bytes needed:
@@ -582,15 +580,9 @@ void __init sme_enable(struct boot_params *bp)
 	 * identity mapped, so we must obtain the address to the SME command
 	 * line argument data using rip-relative addressing.
 	 */
-	asm ("lea sme_cmdline_arg(%%rip), %0"
-	     : "=r" (cmdline_arg)
-	     : "p" (sme_cmdline_arg));
-	asm ("lea sme_cmdline_on(%%rip), %0"
-	     : "=r" (cmdline_on)
-	     : "p" (sme_cmdline_on));
-	asm ("lea sme_cmdline_off(%%rip), %0"
-	     : "=r" (cmdline_off)
-	     : "p" (sme_cmdline_off));
+	asm ("lea %a1, %0" : "=r" (cmdline_arg) : "i" (sme_cmdline_arg));
+	asm ("lea %a1, %0" : "=r" (cmdline_on) : "i" (sme_cmdline_on));
+	asm ("lea %a1, %0" : "=r" (cmdline_off) : "i" (sme_cmdline_off));
 
 	if (IS_ENABLED(CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT))
 		active_by_default = true;
-- 
2.41.0

Re: [PATCH] x86/mm/encrypt: Use %a asm operand modifier to obtain %rip-relative address

[Borislav Petkov]

On Mon, Nov 20, 2023 at 04:33:50PM +0100, Uros Bizjak wrote:
> The "a" asm operand modifier substitutes a memory reference, with the
> actual operand treated as address.  For x86_64, when a symbol is
> provided, the "a" modifier emits "sym(%rip)" instead of "sym".
> 
> Clang allows only "i" and "r" operand constraints with an "a" modifier,
> so the patch normalizes the modifier/constraint pair to "a"/"i"

s/the patch normalizes/normalize/

> which is consistent between both compilers.
> 
> No functional change intended.
> 
> Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
> Cc: Dave Hansen <dave.hansen@linux.intel.com>
> Cc: Andy Lutomirski <luto@kernel.org>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Ingo Molnar <mingo@kernel.org>
> Cc: Borislav Petkov <bp@alien8.de>
> Cc: "H. Peter Anvin" <hpa@zytor.com>
> Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
> ---
>  arch/x86/mm/mem_encrypt_identity.c | 16 ++++------------
>  1 file changed, 4 insertions(+), 12 deletions(-)
> 
> diff --git a/arch/x86/mm/mem_encrypt_identity.c b/arch/x86/mm/mem_encrypt_identity.c
> index d73aeb16417f..6a351fdd1b39 100644
> --- a/arch/x86/mm/mem_encrypt_identity.c
> +++ b/arch/x86/mm/mem_encrypt_identity.c
> @@ -346,9 +346,7 @@ void __init sme_encrypt_kernel(struct boot_params *bp)
>  	 * We're running identity mapped, so we must obtain the address to the
>  	 * SME encryption workarea using rip-relative addressing.
>  	 */
> -	asm ("lea sme_workarea(%%rip), %0"
> -	     : "=r" (workarea_start)
> -	     : "p" (sme_workarea));
> +	asm ("lea %a1, %0" : "=r" (workarea_start) : "i" (sme_workarea));

Yeah, I saw that particular subthread today.

Are you sure this "a" modifier DTRT with all gcc version we support?

I.e., from 5.1 onwards...

Just making sure.

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette

Re: [PATCH] x86/mm/encrypt: Use %a asm operand modifier to obtain %rip-relative address

[Uros Bizjak]

On Mon, Nov 20, 2023 at 6:15 PM Borislav Petkov <bp@alien8.de> wrote:
>
> On Mon, Nov 20, 2023 at 04:33:50PM +0100, Uros Bizjak wrote:
> > The "a" asm operand modifier substitutes a memory reference, with the
> > actual operand treated as address.  For x86_64, when a symbol is
> > provided, the "a" modifier emits "sym(%rip)" instead of "sym".
> >
> > Clang allows only "i" and "r" operand constraints with an "a" modifier,
> > so the patch normalizes the modifier/constraint pair to "a"/"i"
>
> s/the patch normalizes/normalize/
>
> > which is consistent between both compilers.
> >
> > No functional change intended.
> >
> > Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
> > Cc: Dave Hansen <dave.hansen@linux.intel.com>
> > Cc: Andy Lutomirski <luto@kernel.org>
> > Cc: Peter Zijlstra <peterz@infradead.org>
> > Cc: Thomas Gleixner <tglx@linutronix.de>
> > Cc: Ingo Molnar <mingo@kernel.org>
> > Cc: Borislav Petkov <bp@alien8.de>
> > Cc: "H. Peter Anvin" <hpa@zytor.com>
> > Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
> > ---
> >  arch/x86/mm/mem_encrypt_identity.c | 16 ++++------------
> >  1 file changed, 4 insertions(+), 12 deletions(-)
> >
> > diff --git a/arch/x86/mm/mem_encrypt_identity.c b/arch/x86/mm/mem_encrypt_identity.c
> > index d73aeb16417f..6a351fdd1b39 100644
> > --- a/arch/x86/mm/mem_encrypt_identity.c
> > +++ b/arch/x86/mm/mem_encrypt_identity.c
> > @@ -346,9 +346,7 @@ void __init sme_encrypt_kernel(struct boot_params *bp)
> >        * We're running identity mapped, so we must obtain the address to the
> >        * SME encryption workarea using rip-relative addressing.
> >        */
> > -     asm ("lea sme_workarea(%%rip), %0"
> > -          : "=r" (workarea_start)
> > -          : "p" (sme_workarea));
> > +     asm ("lea %a1, %0" : "=r" (workarea_start) : "i" (sme_workarea));
>
> Yeah, I saw that particular subthread today.
>
> Are you sure this "a" modifier DTRT with all gcc version we support?
>
> I.e., from 5.1 onwards...

Yes [1].

[1] https://godbolt.org/z/aWe7b16rT

Thanks,
Uros.

Re: [PATCH] x86/mm/encrypt: Use %a asm operand modifier to obtain %rip-relative address

[Kirill A. Shutemov]

On Mon, Nov 20, 2023 at 08:58:29PM +0100, Uros Bizjak wrote:
> On Mon, Nov 20, 2023 at 6:15 PM Borislav Petkov <bp@alien8.de> wrote:
> >
> > On Mon, Nov 20, 2023 at 04:33:50PM +0100, Uros Bizjak wrote:
> > > The "a" asm operand modifier substitutes a memory reference, with the
> > > actual operand treated as address.  For x86_64, when a symbol is
> > > provided, the "a" modifier emits "sym(%rip)" instead of "sym".
> > >
> > > Clang allows only "i" and "r" operand constraints with an "a" modifier,
> > > so the patch normalizes the modifier/constraint pair to "a"/"i"
> >
> > s/the patch normalizes/normalize/
> >
> > > which is consistent between both compilers.
> > >
> > > No functional change intended.
> > >
> > > Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
> > > Cc: Dave Hansen <dave.hansen@linux.intel.com>
> > > Cc: Andy Lutomirski <luto@kernel.org>
> > > Cc: Peter Zijlstra <peterz@infradead.org>
> > > Cc: Thomas Gleixner <tglx@linutronix.de>
> > > Cc: Ingo Molnar <mingo@kernel.org>
> > > Cc: Borislav Petkov <bp@alien8.de>
> > > Cc: "H. Peter Anvin" <hpa@zytor.com>
> > > Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
> > > ---
> > >  arch/x86/mm/mem_encrypt_identity.c | 16 ++++------------
> > >  1 file changed, 4 insertions(+), 12 deletions(-)
> > >
> > > diff --git a/arch/x86/mm/mem_encrypt_identity.c b/arch/x86/mm/mem_encrypt_identity.c
> > > index d73aeb16417f..6a351fdd1b39 100644
> > > --- a/arch/x86/mm/mem_encrypt_identity.c
> > > +++ b/arch/x86/mm/mem_encrypt_identity.c
> > > @@ -346,9 +346,7 @@ void __init sme_encrypt_kernel(struct boot_params *bp)
> > >        * We're running identity mapped, so we must obtain the address to the
> > >        * SME encryption workarea using rip-relative addressing.
> > >        */
> > > -     asm ("lea sme_workarea(%%rip), %0"
> > > -          : "=r" (workarea_start)
> > > -          : "p" (sme_workarea));
> > > +     asm ("lea %a1, %0" : "=r" (workarea_start) : "i" (sme_workarea));
> >
> > Yeah, I saw that particular subthread today.
> >
> > Are you sure this "a" modifier DTRT with all gcc version we support?
> >
> > I.e., from 5.1 onwards...
> 
> Yes [1].
> 
> [1] https://godbolt.org/z/aWe7b16rT

But Clang generates RIP-relative load only starting from version 15.
Clange 11 claimed to be supported.

-- 
  Kiryl Shutsemau / Kirill A. Shutemov

Re: [PATCH] x86/mm/encrypt: Use %a asm operand modifier to obtain %rip-relative address

[Uros Bizjak]

On Tue, Nov 21, 2023 at 10:05 AM Kirill A. Shutemov
<kirill@shutemov.name> wrote:
>
> On Mon, Nov 20, 2023 at 08:58:29PM +0100, Uros Bizjak wrote:
> > On Mon, Nov 20, 2023 at 6:15 PM Borislav Petkov <bp@alien8.de> wrote:
> > >
> > > On Mon, Nov 20, 2023 at 04:33:50PM +0100, Uros Bizjak wrote:
> > > > The "a" asm operand modifier substitutes a memory reference, with the
> > > > actual operand treated as address.  For x86_64, when a symbol is
> > > > provided, the "a" modifier emits "sym(%rip)" instead of "sym".
> > > >
> > > > Clang allows only "i" and "r" operand constraints with an "a" modifier,
> > > > so the patch normalizes the modifier/constraint pair to "a"/"i"
> > >
> > > s/the patch normalizes/normalize/
> > >
> > > > which is consistent between both compilers.
> > > >
> > > > No functional change intended.
> > > >
> > > > Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
> > > > Cc: Dave Hansen <dave.hansen@linux.intel.com>
> > > > Cc: Andy Lutomirski <luto@kernel.org>
> > > > Cc: Peter Zijlstra <peterz@infradead.org>
> > > > Cc: Thomas Gleixner <tglx@linutronix.de>
> > > > Cc: Ingo Molnar <mingo@kernel.org>
> > > > Cc: Borislav Petkov <bp@alien8.de>
> > > > Cc: "H. Peter Anvin" <hpa@zytor.com>
> > > > Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
> > > > ---
> > > >  arch/x86/mm/mem_encrypt_identity.c | 16 ++++------------
> > > >  1 file changed, 4 insertions(+), 12 deletions(-)
> > > >
> > > > diff --git a/arch/x86/mm/mem_encrypt_identity.c b/arch/x86/mm/mem_encrypt_identity.c
> > > > index d73aeb16417f..6a351fdd1b39 100644
> > > > --- a/arch/x86/mm/mem_encrypt_identity.c
> > > > +++ b/arch/x86/mm/mem_encrypt_identity.c
> > > > @@ -346,9 +346,7 @@ void __init sme_encrypt_kernel(struct boot_params *bp)
> > > >        * We're running identity mapped, so we must obtain the address to the
> > > >        * SME encryption workarea using rip-relative addressing.
> > > >        */
> > > > -     asm ("lea sme_workarea(%%rip), %0"
> > > > -          : "=r" (workarea_start)
> > > > -          : "p" (sme_workarea));
> > > > +     asm ("lea %a1, %0" : "=r" (workarea_start) : "i" (sme_workarea));
> > >
> > > Yeah, I saw that particular subthread today.
> > >
> > > Are you sure this "a" modifier DTRT with all gcc version we support?
> > >
> > > I.e., from 5.1 onwards...
> >
> > Yes [1].
> >
> > [1] https://godbolt.org/z/aWe7b16rT
>
> But Clang generates RIP-relative load only starting from version 15.
> Clange 11 claimed to be supported.

Huh, what a bummer...

The patch is retracted then.

Thanks,
Uros.