linux-kernel - Re: [PATCH v3 1/2] x86/sev: enforce RIP-relative accesses in early SEV/SME code

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Message-ID: <4ljfvg7c23g2wx4hcqz6x6tx7uvp6fffayqvu4ptsmfqajlujr@zngokbd2awma>
Date: Wed, 31 Jan 2024 10:20:28 +0200
From: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To: Kevin Loughlin <kevinloughlin@...gle.com>
Cc: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, 
	Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org, 
	Nick Desaulniers <ndesaulniers@...gle.com>, Justin Stitt <justinstitt@...gle.com>, 
	Tom Lendacky <thomas.lendacky@....com>, Pankaj Gupta <pankaj.gupta@....com>, 
	Hou Wenlong <houwenlong.hwl@...group.com>, Ard Biesheuvel <ardb@...nel.org>, 
	Dionna Glaze <dionnaglaze@...gle.com>, Brijesh Singh <brijesh.singh@....com>, 
	Michael Roth <michael.roth@....com>, linux-kernel@...r.kernel.org, llvm@...ts.linux.dev, 
	linux-coco@...ts.linux.dev, Ashish Kalra <ashish.kalra@....com>, 
	Andi Kleen <ak@...ux.intel.com>, Adam Dunlap <acdunlap@...gle.com>, 
	Peter Gonda <pgonda@...gle.com>, Jacob Xu <jacobhxu@...gle.com>, 
	Sidharth Telang <sidtelang@...gle.com>
Subject: Re: [PATCH v3 1/2] x86/sev: enforce RIP-relative accesses in early
 SEV/SME code

On Tue, Jan 30, 2024 at 10:08:44PM +0000, Kevin Loughlin wrote:
> diff --git a/arch/x86/include/asm/mem_encrypt.h b/arch/x86/include/asm/mem_encrypt.h
> index 359ada486fa9..b65e66ee79c4 100644
> --- a/arch/x86/include/asm/mem_encrypt.h
> +++ b/arch/x86/include/asm/mem_encrypt.h
> @@ -17,6 +17,20 @@
>  
>  #include <asm/bootparam.h>
>  
> +/*
> + * Like the address operator "&", evaluates to the address of a LHS variable
> + * "var", but also enforces the use of RIP-relative logic. This macro can be
> + * used to safely access global data variables prior to kernel relocation.
> + */
> +#define RIP_RELATIVE_ADDR(var)		\
> +({					\
> +	void *rip_rel_ptr;		\
> +	asm ("lea "#var"(%%rip), %0"	\
> +		: "=r" (rip_rel_ptr)	\
> +		: "p" (&var));		\
> +	rip_rel_ptr;			\
> +})
> +

I don't think it is the right place for the macro. The next patch uses for
things unrelated to memory encryption.

> @@ -239,14 +244,14 @@ unsigned long __head __startup_64(unsigned long physaddr,
>  	 */
>  
>  	next_pgt_ptr = fixup_pointer(&next_early_pgt, physaddr);
> -	pud = fixup_pointer(early_dynamic_pgts[(*next_pgt_ptr)++], physaddr);
> -	pmd = fixup_pointer(early_dynamic_pgts[(*next_pgt_ptr)++], physaddr);
> +	early_dynamic_pgts_ptr = fixup_pointer(early_dynamic_pgts, physaddr);
> +	pud = (pudval_t *) early_dynamic_pgts_ptr[(*next_pgt_ptr)++];
> +	pmd = (pmdval_t *) early_dynamic_pgts_ptr[(*next_pgt_ptr)++];
>  

This change doesn't belong to this patch. Maybe move it into the next
patch and combine with removing fixup_pointer().

-- 
  Kiryl Shutsemau / Kirill A. Shutemov