Re: [PATCH v8 1/2] x86/mm: add .bss..decrypted section to hold shared variables

[Brijesh Singh]

On 09/14/2018 09:12 AM, Borislav Petkov wrote:
> On Fri, Sep 14, 2018 at 02:17:05PM +0200, Thomas Gleixner wrote:
> > > The sme_encrypt_kernel() does not have access to pmd (after pointer
> > > fixup is applied). You can extend the sme_encrypt_kernel() to pass an
> > > additional arguments but then we start getting in include hell. The pmd
> > > is defined as "pmdval_t". If we extend the sme_encrypt_kernel() then
> > > asm/mem_encrypt.h need to include the header file which defines
> > > "pmdval_t". Adding the 'asm/pgtable_type.h' was causing all kind of
> > > compilation errors. I didn't spend much time on it. IMO, we really don't
> > > need to go in this path unless we see some value from doing this.
> >
> > Keep it here then.
>
> *For what is worth*, a simple forward declaration works. I've taken the
> 64-bit forward declaration of pmdval_t as SME is 64-bit only anyway.
>
> The below diff ontop passes the mandatory all*config smoke builds:
>
> ---
>   arch/x86/include/asm/mem_encrypt.h |  6 ++++--
>   arch/x86/kernel/head64.c           | 18 +-----------------
>   arch/x86/mm/mem_encrypt_identity.c | 18 +++++++++++++++++-
>   3 files changed, 22 insertions(+), 20 deletions(-)
>
> diff --git a/arch/x86/include/asm/mem_encrypt.h b/arch/x86/include/asm/mem_encrypt.h
> index 616f8e637bc3..67c0e6cfdfb3 100644
> --- a/arch/x86/include/asm/mem_encrypt.h
> +++ b/arch/x86/include/asm/mem_encrypt.h
> @@ -19,6 +19,8 @@
>   
>   #include <asm/bootparam.h>
>   
> +typedef unsigned long pmdval_t;
> +
>   #ifdef CONFIG_AMD_MEM_ENCRYPT
>   
>   extern u64 sme_me_mask;
> @@ -40,7 +42,7 @@ void __init sme_unmap_bootdata(char *real_mode_data);
>   
>   void __init sme_early_init(void);
>   
> -void __init sme_encrypt_kernel(struct boot_params *bp);
> +void __init sme_encrypt_kernel(struct boot_params *bp, pmdval_t *pmd);
>   void __init sme_enable(struct boot_params *bp);
>   
>   int __init early_set_memory_decrypted(unsigned long vaddr, unsigned long size);
> @@ -69,7 +71,7 @@ static inline void __init sme_unmap_bootdata(char *real_mode_data) { }
>   
>   static inline void __init sme_early_init(void) { }
>   
> -static inline void __init sme_encrypt_kernel(struct boot_params *bp) { }
> +static inline void __init sme_encrypt_kernel(struct boot_params *bp, pmdval_t *pmd) { }
>   static inline void __init sme_enable(struct boot_params *bp) { }
>   
>   static inline bool sme_active(void) { return false; }
> diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c
> index c16af27eb23f..6f8e9b534e80 100644
> --- a/arch/x86/kernel/head64.c
> +++ b/arch/x86/kernel/head64.c
> @@ -112,7 +112,6 @@ static bool __head check_la57_support(unsigned long physaddr)
>   unsigned long __head __startup_64(unsigned long physaddr,
>   				  struct boot_params *bp)
>   {
> -	unsigned long vaddr, vaddr_end;
>   	unsigned long load_delta, *p;
>   	unsigned long pgtable_flags;
>   	pgdval_t *pgd;
> @@ -233,22 +232,7 @@ unsigned long __head __startup_64(unsigned long physaddr,
>   	*fixup_long(&phys_base, physaddr) += load_delta - sme_get_me_mask();
>   
>   	/* Encrypt the kernel and related (if SME is active) */
> -	sme_encrypt_kernel(bp);
> -
> -	/*
> -	 * Clear the memory encryption mask from the .bss..decrypted section.
> -	 * The bss section will be memset to zero later in the initialization so
> -	 * there is no need to zero it after changing the memory encryption
> -	 * attribute.
> -	 */
> -	if (mem_encrypt_active()) {
> -		vaddr = (unsigned long)__start_bss_decrypted;
> -		vaddr_end = (unsigned long)__end_bss_decrypted;
> -		for (; vaddr < vaddr_end; vaddr += PMD_SIZE) {
> -			i = pmd_index(vaddr);
> -			pmd[i] -= sme_get_me_mask();
> -		}
> -	}
> +	sme_encrypt_kernel(bp, pmd);
>   
>   	/*
>   	 * Return the SME encryption mask (if SME is active) to be used as a
> diff --git a/arch/x86/mm/mem_encrypt_identity.c b/arch/x86/mm/mem_encrypt_identity.c
> index a19ef1a416ff..9dbc145d10f8 100644
> --- a/arch/x86/mm/mem_encrypt_identity.c
> +++ b/arch/x86/mm/mem_encrypt_identity.c
> @@ -267,15 +267,17 @@ static unsigned long __init sme_pgtable_calc(unsigned long len)
>   	return entries + tables;
>   }
>   
> -void __init sme_encrypt_kernel(struct boot_params *bp)
> +void __init sme_encrypt_kernel(struct boot_params *bp, pmdval_t *pmd)
>   {
>   	unsigned long workarea_start, workarea_end, workarea_len;
>   	unsigned long execute_start, execute_end, execute_len;
>   	unsigned long kernel_start, kernel_end, kernel_len;
>   	unsigned long initrd_start, initrd_end, initrd_len;
>   	struct sme_populate_pgd_data ppd;
> +	unsigned long vaddr, vaddr_end;
>   	unsigned long pgtable_area_len;
>   	unsigned long decrypted_base;
> +	int i;
>   
>   	if (!sme_active())
>   		return;
> @@ -467,6 +469,20 @@ void __init sme_encrypt_kernel(struct boot_params *bp)
>   
>   	/* Flush the TLB - no globals so cr3 is enough */
>   	native_write_cr3(__native_read_cr3());
> +
> +	/*
> +	 * Clear the memory encryption mask from the .bss..decrypted section.
> +	 * The bss section will be memset to zero later in the initialization so
> +	 * there is no need to zero it after changing the memory encryption
> +	 * attribute.
> +	 */
> +	vaddr = (unsigned long)__start_bss_decrypted;
> +	vaddr_end = (unsigned long)__end_bss_decrypted;
> +
> +	for (; vaddr < vaddr_end; vaddr += PMD_SIZE) {
> +		i = pmd_index(vaddr);
> +		pmd[i] -= sme_get_me_mask();
> +	}
>   }


The above code will never get executed for the SEV case.

See if (!sme_active()) check in the start of function.

If we decide to go on this patch, then we have to do something like
this:

sme_encrypt_kernel(...)
{
	if (!mem_encrypt_active())
		return;

	if (sev_active())
		goto out;

	/* Do kernel and initrd in-place encrypts for SME only case */
	.....
	.....

out:
	/* Clear the C-bit from .bss..decrypted section */
	...
	...
}


>   
>   void __init sme_enable(struct boot_params *bp)