Re: [RFC PATCH v4 21/28] x86: Check for memory encryption on the APs

Borislav Petkov
2017-02-27T19:14:17Z

On Thu, Feb 16, 2017 at 09:46:47AM -0600, Tom Lendacky wrote:
> Add support to check if memory encryption is active in the kernel and that
> it has been enabled on the AP. If memory encryption is active in the kernel
> but has not been enabled on the AP, then set the SYS_CFG MSR bit to enable
> memory encryption on that AP and allow the AP to continue start up.
>
> Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
> ---
> arch/x86/include/asm/realmode.h | 12 ++++++++++++
> arch/x86/realmode/init.c | 4 ++++
> arch/x86/realmode/rm/trampoline_64.S | 17 +++++++++++++++++
> 3 files changed, 33 insertions(+)
>
> diff --git a/arch/x86/include/asm/realmode.h b/arch/x86/include/asm/realmode.h
> index 230e190..4f7ef53 100644
> --- a/arch/x86/include/asm/realmode.h
> +++ b/arch/x86/include/asm/realmode.h
> @@ -1,6 +1,15 @@
> #ifndef _ARCH_X86_REALMODE_H
> #define _ARCH_X86_REALMODE_H
>
> +/*
> + * Flag bit definitions for use with the flags field of the trampoline header
> + * int the CONFIG_X86_64 variant.

s/int/in/

> + */
> +#define TH_FLAGS_SME_ACTIVE_BIT 0
> +#define TH_FLAGS_SME_ACTIVE BIT(TH_FLAGS_SME_ACTIVE_BIT)
> +
> +#ifndef __ASSEMBLY__
> +
> #include <linux/types.h>
> #include <asm/io.h>
>
> @@ -38,6 +47,7 @@ struct trampoline_header {
> u64 start;
> u64 efer;
> u32 cr4;
> + u32 flags;
> #endif
> };
>
> @@ -69,4 +79,6 @@ static inline size_t real_mode_size_needed(void)
> void set_real_mode_mem(phys_addr_t mem, size_t size);
> void reserve_real_mode(void);
>
> +#endif /* __ASSEMBLY__ */
> +
> #endif /* _ARCH_X86_REALMODE_H */
> diff --git a/arch/x86/realmode/init.c b/arch/x86/realmode/init.c
> index 21d7506..5010089 100644
> --- a/arch/x86/realmode/init.c
> +++ b/arch/x86/realmode/init.c
> @@ -102,6 +102,10 @@ static void __init setup_real_mode(void)
> trampoline_cr4_features = &trampoline_header->cr4;
> *trampoline_cr4_features = mmu_cr4_features;
>
> + trampoline_header->flags = 0;
> + if (sme_active())
> + trampoline_header->flags |= TH_FLAGS_SME_ACTIVE;
> +
> trampoline_pgd = (u64 *) __va(real_mode_header->trampoline_pgd);
> trampoline_pgd[0] = trampoline_pgd_entry.pgd;
> trampoline_pgd[511] = init_level4_pgt[511].pgd;
> diff --git a/arch/x86/realmode/rm/trampoline_64.S b/arch/x86/realmode/rm/trampoline_64.S
> index dac7b20..a88c3d1 100644
> --- a/arch/x86/realmode/rm/trampoline_64.S
> +++ b/arch/x86/realmode/rm/trampoline_64.S
> @@ -30,6 +30,7 @@
> #include <asm/msr.h>
> #include <asm/segment.h>
> #include <asm/processor-flags.h>
> +#include <asm/realmode.h>
> #include "realmode.h"
>
> .text
> @@ -92,6 +93,21 @@ ENTRY(startup_32)
> movl %edx, %fs
> movl %edx, %gs
>
> + /* Check for memory encryption support */

Let's add some blurb here about this being a safety net in case BIOS
f*cks up. Which wouldn't be that far-fetched... :-)

> + bt $TH_FLAGS_SME_ACTIVE_BIT, pa_tr_flags
> + jnc .Ldone
> + movl $MSR_K8_SYSCFG, %ecx
> + rdmsr
> + bts $MSR_K8_SYSCFG_MEM_ENCRYPT_BIT, %eax
> + jc .Ldone

--
Regards/Gruss,
Boris.

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