Re: [RFC PATCH v4 28/28] x86: Add support to make use of Secure Memory Encryption

Tom Lendacky
2017-03-07T16:05:00Z

On 3/1/2017 12:40 PM, Borislav Petkov wrote:
> On Thu, Feb 16, 2017 at 09:48:25AM -0600, Tom Lendacky wrote:
>> This patch adds the support to check if SME has been enabled and if
>> memory encryption should be activated (checking of command line option
>> based on the configuration of the default state). If memory encryption
>> is to be activated, then the encryption mask is set and the kernel is
>> encrypted "in place."
>>
>> Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
>> ---
>> arch/x86/kernel/head_64.S | 1 +
>> arch/x86/kernel/mem_encrypt_init.c | 71 +++++++++++++++++++++++++++++++++++-
>> arch/x86/mm/mem_encrypt.c | 2 +
>> 3 files changed, 73 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
>> index edd2f14..e6820e7 100644
>> --- a/arch/x86/kernel/head_64.S
>> +++ b/arch/x86/kernel/head_64.S
>> @@ -97,6 +97,7 @@ startup_64:
>> * Save the returned mask in %r12 for later use.
>> */
>> push %rsi
>> + movq %rsi, %rdi
>> call sme_enable
>> pop %rsi
>> movq %rax, %r12
>> diff --git a/arch/x86/kernel/mem_encrypt_init.c b/arch/x86/kernel/mem_encrypt_init.c
>> index 07cbb90..35c5e3d 100644
>> --- a/arch/x86/kernel/mem_encrypt_init.c
>> +++ b/arch/x86/kernel/mem_encrypt_init.c
>> @@ -19,6 +19,12 @@
>> #include <linux/mm.h>
>>
>> #include <asm/sections.h>
>> +#include <asm/processor-flags.h>
>> +#include <asm/msr.h>
>> +#include <asm/cmdline.h>
>> +
>> +static char sme_cmdline_arg_on[] __initdata = "mem_encrypt=on";
>> +static char sme_cmdline_arg_off[] __initdata = "mem_encrypt=off";
>>
>> extern void sme_encrypt_execute(unsigned long, unsigned long, unsigned long,
>> void *, pgd_t *);
>> @@ -217,8 +223,71 @@ unsigned long __init sme_get_me_mask(void)
>> return sme_me_mask;
>> }
>>
>> -unsigned long __init sme_enable(void)
>> +unsigned long __init sme_enable(void *boot_data)
>
> unsigned long __init sme_enable(struct boot_params *bp)
>
> works too.

Ok, will do.

>
> And then you need to correct the function signature in the
> !CONFIG_AMD_MEM_ENCRYPT case, at the end of this file, too:
>
> unsigned long __init sme_enable(struct boot_params *bp) { return 0; }

Yup, missed that. I'll make it match.

>
>> {
>> + struct boot_params *bp = boot_data;
>> + unsigned int eax, ebx, ecx, edx;
>> + unsigned long cmdline_ptr;
>> + bool enable_if_found;
>> + void *cmdline_arg;
>> + u64 msr;
>> +
>> + /* Check for an AMD processor */
>> + eax = 0;
>> + ecx = 0;
>> + native_cpuid(&eax, &ebx, &ecx, &edx);
>> + if ((ebx != 0x68747541) || (edx != 0x69746e65) || (ecx != 0x444d4163))
>> + goto out;
>> +
>> + /* Check for the SME support leaf */
>> + eax = 0x80000000;
>> + ecx = 0;
>> + native_cpuid(&eax, &ebx, &ecx, &edx);
>> + if (eax < 0x8000001f)
>> + goto out;
>> +
>> + /*
>> + * Check for the SME feature:
>> + * CPUID Fn8000_001F[EAX] - Bit 0
>> + * Secure Memory Encryption support
>> + * CPUID Fn8000_001F[EBX] - Bits 5:0
>> + * Pagetable bit position used to indicate encryption
>> + */
>> + eax = 0x8000001f;
>> + ecx = 0;
>> + native_cpuid(&eax, &ebx, &ecx, &edx);
>> + if (!(eax & 1))
>> + goto out;
>> +
>> + /* Check if SME is enabled */
>> + msr = native_read_msr(MSR_K8_SYSCFG);
>
> This native_read_msr() wankery is adding this check:
>
> if (msr_tracepoint_active(__tracepoint_read_msr))
>
> and here it is clearly too early for tracepoints. Please use __rdmsr()
> which is purely doing the MSR operation. (... and exception handling for

Ah, good catch. I'll switch to __rdmsr().

> when the RDMSR itself raises an exception but we're very early here too
> so the MSR better be there, otherwise we'll blow up).

Yes, it will be there if SME support is indicated in the CPUID result.

>
>> + if (!(msr & MSR_K8_SYSCFG_MEM_ENCRYPT))
>> + goto out;
>> +
>> + /*
>> + * Fixups have not been to applied phys_base yet, so we must obtain
>
> ... not been applied to phys_base yet ...

Yup.

>
>> + * the address to the SME command line option in the following way.
>> + */
>> + if (IS_ENABLED(CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT)) {
>> + asm ("lea sme_cmdline_arg_off(%%rip), %0"
>> + : "=r" (cmdline_arg)
>> + : "p" (sme_cmdline_arg_off));
>> + enable_if_found = false;
>> + } else {
>> + asm ("lea sme_cmdline_arg_on(%%rip), %0"
>> + : "=r" (cmdline_arg)
>> + : "p" (sme_cmdline_arg_on));
>> + enable_if_found = true;
>> + }
>> +
>> + cmdline_ptr = bp->hdr.cmd_line_ptr | ((u64)bp->ext_cmd_line_ptr << 32);
>> +
>> + if (cmdline_find_option_bool((char *)cmdline_ptr, cmdline_arg))
>> + sme_me_mask = enable_if_found ? 1UL << (ebx & 0x3f) : 0;
>> + else
>> + sme_me_mask = enable_if_found ? 0 : 1UL << (ebx & 0x3f);
>
> I have a better idea: you can copy __cmdline_find_option() +
> cmdline_find_option() to arch/x86/lib/cmdline.c in a pre-patch. Then,
> pass in a buffer and check for "on" and "off". This way you don't
> have to misuse the _bool() variant for something which is actually
> "option=argument".

I can do that. Because phys_base hasn't been updated yet, I'll have to
create "on" and "off" constants and get their address in a similar way
to the command line option so that I can do the strncmp properly.

Thanks,
Tom

>
> Thanks.
>

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org. For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: email@kvack.org