Re: [RFC PATCH v4 06/28] x86: Add support to enable SME during early boot processing
From: Tom Lendacky
Date: Tue Feb 21 2017 - 09:56:05 EST
On 2/20/2017 6:51 AM, Borislav Petkov wrote:
On Thu, Feb 16, 2017 at 09:43:19AM -0600, Tom Lendacky wrote:
This patch adds support to the early boot code to use Secure Memory
Encryption (SME). Support is added to update the early pagetables with
the memory encryption mask and to encrypt the kernel in place.
The routines to set the encryption mask and perform the encryption are
stub routines for now with full function to be added in a later patch.
s/full function/functionality/
Ok.
A new file, arch/x86/kernel/mem_encrypt_init.c, is introduced to avoid
adding #ifdefs within arch/x86/kernel/head_64.S and allow
arch/x86/mm/mem_encrypt.c to be removed from the build if SME is not
configured. The mem_encrypt_init.c file will contain the necessary #ifdefs
to allow head_64.S to successfully build and call the SME routines.
That paragraph is superfluous.
I'll remove this, especially since the files will be combined now.
Signed-off-by: Tom Lendacky <thomas.lendacky@xxxxxxx>
---
arch/x86/kernel/Makefile | 2 +
arch/x86/kernel/head_64.S | 46 ++++++++++++++++++++++++++++++++-
arch/x86/kernel/mem_encrypt_init.c | 50 ++++++++++++++++++++++++++++++++++++
3 files changed, 96 insertions(+), 2 deletions(-)
create mode 100644 arch/x86/kernel/mem_encrypt_init.c
diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
index bdcdb3b..33af80a 100644
--- a/arch/x86/kernel/Makefile
+++ b/arch/x86/kernel/Makefile
@@ -140,4 +140,6 @@ ifeq ($(CONFIG_X86_64),y)
obj-$(CONFIG_PCI_MMCONFIG) += mmconf-fam10h_64.o
obj-y += vsmp_64.o
+
+ obj-y += mem_encrypt_init.o
endif
diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
index b467b14..4f8201b 100644
--- a/arch/x86/kernel/head_64.S
+++ b/arch/x86/kernel/head_64.S
@@ -91,6 +91,23 @@ startup_64:
jnz bad_address
/*
+ * Enable Secure Memory Encryption (SME), if supported and enabled.
+ * The real_mode_data address is in %rsi and that register can be
+ * clobbered by the called function so be sure to save it.
+ * Save the returned mask in %r12 for later use.
+ */
+ push %rsi
+ call sme_enable
+ pop %rsi
+ movq %rax, %r12
+
+ /*
+ * Add the memory encryption mask to %rbp to include it in the page
+ * table fixups.
+ */
+ addq %r12, %rbp
+
+ /*
* Fixup the physical addresses in the page table
*/
addq %rbp, early_level4_pgt + (L4_START_KERNEL*8)(%rip)
@@ -113,6 +130,7 @@ startup_64:
shrq $PGDIR_SHIFT, %rax
leaq (PAGE_SIZE + _KERNPG_TABLE)(%rbx), %rdx
+ addq %r12, %rdx
movq %rdx, 0(%rbx,%rax,8)
movq %rdx, 8(%rbx,%rax,8)
@@ -129,6 +147,7 @@ startup_64:
movq %rdi, %rax
shrq $PMD_SHIFT, %rdi
addq $(__PAGE_KERNEL_LARGE_EXEC & ~_PAGE_GLOBAL), %rax
+ addq %r12, %rax
leaq (_end - 1)(%rip), %rcx
shrq $PMD_SHIFT, %rcx
subq %rdi, %rcx
@@ -162,11 +181,25 @@ startup_64:
cmp %r8, %rdi
jne 1b
- /* Fixup phys_base */
+ /*
+ * Fixup phys_base - remove the memory encryption mask from %rbp
+ * to obtain the true physical address.
+ */
+ subq %r12, %rbp
addq %rbp, phys_base(%rip)
+ /*
+ * Encrypt the kernel if SME is active.
+ * The real_mode_data address is in %rsi and that register can be
+ * clobbered by the called function so be sure to save it.
+ */
+ push %rsi
+ call sme_encrypt_kernel
+ pop %rsi
+
.Lskip_fixup:
So if we land on this label because we can skip the fixup due to %rbp
being 0, we will skip sme_encrypt_kernel() too.
I think you need to move the .Lskip_fixup label above the
sme_encrypt_kernel call.
Actually, %rbp will have the encryption bit set in it at the time of the
check so if SME is active we won't take the jump to .Lskip_fixup.
movq $(early_level4_pgt - __START_KERNEL_map), %rax
+ addq %r12, %rax
jmp 1f
ENTRY(secondary_startup_64)
/*
@@ -186,7 +219,16 @@ ENTRY(secondary_startup_64)
/* Sanitize CPU configuration */
call verify_cpu
- movq $(init_level4_pgt - __START_KERNEL_map), %rax
+ /*
+ * Get the SME encryption mask.
+ * The real_mode_data address is in %rsi and that register can be
+ * clobbered by the called function so be sure to save it.
You can say here that sme_get_me_mask puts the mask in %rax, that's why
we do ADD below and not MOV. I know, it is very explicit but this is
boot asm and I'd prefer for it to be absolutely clear.
Ok, I can be explicit on this.
+ */
+ push %rsi
+ call sme_get_me_mask
+ pop %rsi
+
+ addq $(init_level4_pgt - __START_KERNEL_map), %rax
1:
...
+#else /* !CONFIG_AMD_MEM_ENCRYPT */
+
+void __init sme_encrypt_kernel(void)
+{
+}
+
+unsigned long __init sme_get_me_mask(void)
+{
+ return 0;
+}
+
+unsigned long __init sme_enable(void)
+{
+ return 0;
+}
Do that:
void __init sme_encrypt_kernel(void) { }
unsigned long __init sme_get_me_mask(void) { return 0; }
unsigned long __init sme_enable(void) { return 0; }
to save some lines.
No problem.
Thanks,
Tom