On 5/19/2017 6:27 AM, Borislav Petkov wrote:
On Tue, Apr 18, 2017 at 04:22:23PM -0500, Tom Lendacky wrote:
Add 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@xxxxxxx>
---
arch/x86/kernel/head_64.S | 1 +
arch/x86/mm/mem_encrypt.c | 83 +++++++++++++++++++++++++++++++++++++++++++--
2 files changed, 80 insertions(+), 4 deletions(-)
...
+unsigned long __init sme_enable(struct boot_params *bp)
{
+ const char *cmdline_ptr, *cmdline_arg, *cmdline_on, *cmdline_off;
+ unsigned int eax, ebx, ecx, edx;
+ unsigned long me_mask;
+ bool active_by_default;
+ char buffer[16];
+ u64 msr;
+
+ /* 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;
<---- newline here.
+ me_mask = 1UL << (ebx & 0x3f);
+
+ /* Check if SME is enabled */
+ msr = __rdmsr(MSR_K8_SYSCFG);
+ if (!(msr & MSR_K8_SYSCFG_MEM_ENCRYPT))
+ goto out;
+
+ /*
+ * Fixups have not been applied to phys_base yet, so we must obtain
+ * the address to the SME command line option data in the following
+ * way.
+ */
+ 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));
+
+ if (IS_ENABLED(CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT))
+ active_by_default = true;
+ else
+ active_by_default = false;
+
+ cmdline_ptr = (const char *)((u64)bp->hdr.cmd_line_ptr |
+ ((u64)bp->ext_cmd_line_ptr << 32));
+
+ cmdline_find_option(cmdline_ptr, cmdline_arg, buffer, sizeof(buffer));
+
+ if (strncmp(buffer, cmdline_on, sizeof(buffer)) == 0)
+ sme_me_mask = me_mask;
Why doesn't simply
if (!strncmp(buffer, "on", 2))
...
work?
In this case we're running identity mapped and the "on" constant ends up
as kernel address (0xffffffff81...) which results in a segfault.
Thanks,
Tom
