[PATCH v5 29/32] x86/mm: Add support to encrypt the kernel in-place

Tom Lendacky
2017-04-18T21:22:17Z

Add the support to encrypt the kernel in-place. This is done by creating
new page mappings for the kernel - a decrypted write-protected mapping
and an encrypted mapping. The kernel is encrypted by copying it through
a temporary buffer.

Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
---
arch/x86/include/asm/mem_encrypt.h | 6 +
arch/x86/mm/Makefile | 2
arch/x86/mm/mem_encrypt.c | 262 ++++++++++++++++++++++++++++++++++++
arch/x86/mm/mem_encrypt_boot.S | 151 +++++++++++++++++++++
4 files changed, 421 insertions(+)
create mode 100644 arch/x86/mm/mem_encrypt_boot.S

diff --git a/arch/x86/include/asm/mem_encrypt.h b/arch/x86/include/asm/mem_encrypt.h
index b406df2..8f6f9b4 100644
--- a/arch/x86/include/asm/mem_encrypt.h
+++ b/arch/x86/include/asm/mem_encrypt.h
@@ -31,6 +31,12 @@ static inline u64 sme_dma_mask(void)
return ((u64)sme_me_mask << 1) - 1;
}

+void sme_encrypt_execute(unsigned long encrypted_kernel_vaddr,
+ unsigned long decrypted_kernel_vaddr,
+ unsigned long kernel_len,
+ unsigned long encryption_wa,
+ unsigned long encryption_pgd);
+
void __init sme_early_encrypt(resource_size_t paddr,
unsigned long size);
void __init sme_early_decrypt(resource_size_t paddr,
diff --git a/arch/x86/mm/Makefile b/arch/x86/mm/Makefile
index 9e13841..0633142 100644
--- a/arch/x86/mm/Makefile
+++ b/arch/x86/mm/Makefile
@@ -38,3 +38,5 @@ obj-$(CONFIG_NUMA_EMU) += numa_emulation.o
obj-$(CONFIG_X86_INTEL_MPX) += mpx.o
obj-$(CONFIG_X86_INTEL_MEMORY_PROTECTION_KEYS) += pkeys.o
obj-$(CONFIG_RANDOMIZE_MEMORY) += kaslr.o
+
+obj-$(CONFIG_AMD_MEM_ENCRYPT) += mem_encrypt_boot.o
diff --git a/arch/x86/mm/mem_encrypt.c b/arch/x86/mm/mem_encrypt.c
index 30b07a3..0ff41a4 100644
--- a/arch/x86/mm/mem_encrypt.c
+++ b/arch/x86/mm/mem_encrypt.c
@@ -24,6 +24,7 @@
#include <asm/setup.h>
#include <asm/bootparam.h>
#include <asm/cacheflush.h>
+#include <asm/sections.h>

/*
* Since SME related variables are set early in the boot process they must
@@ -216,8 +217,269 @@ void swiotlb_set_mem_attributes(void *vaddr, unsigned long size)
set_memory_decrypted((unsigned long)vaddr, size >> PAGE_SHIFT);
}

+void __init sme_clear_pgd(pgd_t *pgd_base, unsigned long start,
+ unsigned long end)
+{
+ unsigned long addr = start;
+ pgdval_t *pgd_p;
+
+ while (addr < end) {
+ unsigned long pgd_end;
+
+ pgd_end = (addr & PGDIR_MASK) + PGDIR_SIZE;
+ if (pgd_end > end)
+ pgd_end = end;
+
+ pgd_p = (pgdval_t *)pgd_base + pgd_index(addr);
+ *pgd_p = 0;
+
+ addr = pgd_end;
+ }
+}
+
+#define PGD_FLAGS _KERNPG_TABLE_NOENC
+#define PUD_FLAGS _KERNPG_TABLE_NOENC
+#define PMD_FLAGS (__PAGE_KERNEL_LARGE_EXEC & ~_PAGE_GLOBAL)
+
+static void __init *sme_populate_pgd(pgd_t *pgd_base, void *pgtable_area,
+ unsigned long vaddr, pmdval_t pmd_val)
+{
+ pgdval_t pgd, *pgd_p;
+ pudval_t pud, *pud_p;
+ pmdval_t pmd, *pmd_p;
+
+ pgd_p = (pgdval_t *)pgd_base + pgd_index(vaddr);
+ pgd = *pgd_p;
+ if (pgd) {
+ pud_p = (pudval_t *)(pgd & ~PTE_FLAGS_MASK);
+ } else {
+ pud_p = pgtable_area;
+ memset(pud_p, 0, sizeof(*pud_p) * PTRS_PER_PUD);
+ pgtable_area += sizeof(*pud_p) * PTRS_PER_PUD;
+
+ *pgd_p = (pgdval_t)pud_p + PGD_FLAGS;
+ }
+
+ pud_p += pud_index(vaddr);
+ pud = *pud_p;
+ if (pud) {
+ if (pud & _PAGE_PSE)
+ goto out;
+
+ pmd_p = (pmdval_t *)(pud & ~PTE_FLAGS_MASK);
+ } else {
+ pmd_p = pgtable_area;
+ memset(pmd_p, 0, sizeof(*pmd_p) * PTRS_PER_PMD);
+ pgtable_area += sizeof(*pmd_p) * PTRS_PER_PMD;
+
+ *pud_p = (pudval_t)pmd_p + PUD_FLAGS;
+ }
+
+ pmd_p += pmd_index(vaddr);
+ pmd = *pmd_p;
+ if (!pmd || !(pmd & _PAGE_PSE))
+ *pmd_p = pmd_val;
+
+out:
+ return pgtable_area;
+}
+
+static unsigned long __init sme_pgtable_calc(unsigned long len)
+{
+ unsigned long pud_tables, pmd_tables;
+ unsigned long total = 0;
+
+ /*
+ * Perform a relatively simplistic calculation of the pagetable
+ * entries that are needed. That mappings will be covered by 2MB
+ * PMD entries so we can conservatively calculate the required
+ * number of PUD and PMD structures needed to perform the mappings.
+ * Incrementing the count for each covers the case where the
+ * addresses cross entries.
+ */
+ pud_tables = ALIGN(len, PGDIR_SIZE) / PGDIR_SIZE;
+ pud_tables++;
+ pmd_tables = ALIGN(len, PUD_SIZE) / PUD_SIZE;
+ pmd_tables++;
+
+ total += pud_tables * sizeof(pud_t) * PTRS_PER_PUD;
+ total += pmd_tables * sizeof(pmd_t) * PTRS_PER_PMD;
+
+ /*
+ * Now calculate the added pagetable structures needed to populate
+ * the new pagetables.
+ */
+ pud_tables = ALIGN(total, PGDIR_SIZE) / PGDIR_SIZE;
+ pmd_tables = ALIGN(total, PUD_SIZE) / PUD_SIZE;
+
+ total += pud_tables * sizeof(pud_t) * PTRS_PER_PUD;
+ total += pmd_tables * sizeof(pmd_t) * PTRS_PER_PMD;
+
+ return total;
+}
+
void __init sme_encrypt_kernel(void)
{
+ pgd_t *pgd;
+ void *pgtable_area;
+ unsigned long kernel_start, kernel_end, kernel_len;
+ unsigned long workarea_start, workarea_end, workarea_len;
+ unsigned long execute_start, execute_end, execute_len;
+ unsigned long pgtable_area_len;
+ unsigned long decrypted_base;
+ unsigned long paddr, pmd_flags;
+
+ if (!sme_active())
+ return;
+
+ /*
+ * Prepare for encrypting the kernel by building new pagetables with
+ * the necessary attributes needed to encrypt the kernel in place.
+ *
+ * One range of virtual addresses will map the memory occupied
+ * by the kernel as encrypted.
+ *
+ * Another range of virtual addresses will map the memory occupied
+ * by the kernel as decrypted and write-protected.
+ *
+ * The use of write-protect attribute will prevent any of the
+ * memory from being cached.
+ */
+
+ /* Physical addresses gives us the identity mapped virtual addresses */
+ kernel_start = __pa_symbol(_text);
+ kernel_end = ALIGN(__pa_symbol(_end), PMD_PAGE_SIZE);
+ kernel_len = kernel_end - kernel_start;
+
+ /* Set the encryption workarea to be immediately after the kernel */
+ workarea_start = kernel_end;
+
+ /*
+ * Calculate required number of workarea bytes needed:
+ * executable encryption area size:
+ * stack page (PAGE_SIZE)
+ * encryption routine page (PAGE_SIZE)
+ * intermediate copy buffer (PMD_PAGE_SIZE)
+ * pagetable structures for the encryption of the kernel
+ * pagetable structures for workarea (in case not currently mapped)
+ */
+ execute_start = workarea_start;
+ execute_end = execute_start + (PAGE_SIZE * 2) + PMD_PAGE_SIZE;
+ execute_len = execute_end - execute_start;
+
+ /*
+ * One PGD for both encrypted and decrypted mappings and a set of
+ * PUDs and PMDs for each of the encrypted and decrypted mappings.
+ */
+ pgtable_area_len = sizeof(pgd_t) * PTRS_PER_PGD;
+ pgtable_area_len += sme_pgtable_calc(execute_end - kernel_start) * 2;
+
+ /* PUDs and PMDs needed in the current pagetables for the workarea */
+ pgtable_area_len += sme_pgtable_calc(execute_len + pgtable_area_len);
+
+ /*
+ * The total workarea includes the executable encryption area and
+ * the pagetable area.
+ */
+ workarea_len = execute_len + pgtable_area_len;
+ workarea_end = workarea_start + workarea_len;
+
+ /*
+ * Set the address to the start of where newly created pagetable
+ * structures (PGDs, PUDs and PMDs) will be allocated. New pagetable
+ * structures are created when the workarea is added to the current
+ * pagetables and when the new encrypted and decrypted kernel
+ * mappings are populated.
+ */
+ pgtable_area = (void *)execute_end;
+
+ /*
+ * Make sure the current pagetable structure has entries for
+ * addressing the workarea.
+ */
+ pgd = (pgd_t *)native_read_cr3();
+ paddr = workarea_start;
+ while (paddr < workarea_end) {
+ pgtable_area = sme_populate_pgd(pgd, pgtable_area,
+ paddr,
+ paddr + PMD_FLAGS);
+
+ paddr += PMD_PAGE_SIZE;
+ }
+ native_write_cr3((unsigned long)pgd);
+
+ /*
+ * A new pagetable structure is being built to allow for the kernel
+ * to be encrypted. It starts with an empty PGD that will then be
+ * populated with new PUDs and PMDs as the encrypted and decrypted
+ * kernel mappings are created.
+ */
+ pgd = pgtable_area;
+ memset(pgd, 0, sizeof(*pgd) * PTRS_PER_PGD);
+ pgtable_area += sizeof(*pgd) * PTRS_PER_PGD;
+
+ /* Add encrypted kernel (identity) mappings */
+ pmd_flags = PMD_FLAGS | _PAGE_ENC;
+ paddr = kernel_start;
+ while (paddr < kernel_end) {
+ pgtable_area = sme_populate_pgd(pgd, pgtable_area,
+ paddr,
+ paddr + pmd_flags);
+
+ paddr += PMD_PAGE_SIZE;
+ }
+
+ /*
+ * A different PGD index/entry must be used to get different
+ * pagetable entries for the decrypted mapping. Choose the next
+ * PGD index and convert it to a virtual address to be used as
+ * the base of the mapping.
+ */
+ decrypted_base = (pgd_index(workarea_end) + 1) & (PTRS_PER_PGD - 1);
+ decrypted_base <<= PGDIR_SHIFT;
+
+ /* Add decrypted, write-protected kernel (non-identity) mappings */
+ pmd_flags = (PMD_FLAGS & ~_PAGE_CACHE_MASK) | (_PAGE_PAT | _PAGE_PWT);
+ paddr = kernel_start;
+ while (paddr < kernel_end) {
+ pgtable_area = sme_populate_pgd(pgd, pgtable_area,
+ paddr + decrypted_base,
+ paddr + pmd_flags);
+
+ paddr += PMD_PAGE_SIZE;
+ }
+
+ /* Add decrypted workarea mappings to both kernel mappings */
+ paddr = workarea_start;
+ while (paddr < workarea_end) {
+ pgtable_area = sme_populate_pgd(pgd, pgtable_area,
+ paddr,
+ paddr + PMD_FLAGS);
+
+ pgtable_area = sme_populate_pgd(pgd, pgtable_area,
+ paddr + decrypted_base,
+ paddr + PMD_FLAGS);
+
+ paddr += PMD_PAGE_SIZE;
+ }
+
+ /* Perform the encryption */
+ sme_encrypt_execute(kernel_start, kernel_start + decrypted_base,
+ kernel_len, workarea_start, (unsigned long)pgd);
+
+ /*
+ * At this point we are running encrypted. Remove the mappings for
+ * the decrypted areas - all that is needed for this is to remove
+ * the PGD entry/entries.
+ */
+ sme_clear_pgd(pgd, kernel_start + decrypted_base,
+ kernel_end + decrypted_base);
+
+ sme_clear_pgd(pgd, workarea_start + decrypted_base,
+ workarea_end + decrypted_base);
+
+ /* Flush the TLB - no globals so cr3 is enough */
+ native_write_cr3(native_read_cr3());
}

unsigned long __init sme_enable(void)
diff --git a/arch/x86/mm/mem_encrypt_boot.S b/arch/x86/mm/mem_encrypt_boot.S
new file mode 100644
index 0000000..fb58f9f
--- /dev/null
+++ b/arch/x86/mm/mem_encrypt_boot.S
@@ -0,0 +1,151 @@
+/*
+ * AMD Memory Encryption Support
+ *
+ * Copyright (C) 2016 Advanced Micro Devices, Inc.
+ *
+ * Author: Tom Lendacky <thomas.lendacky@amd.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+
+#include <linux/linkage.h>
+#include <asm/pgtable.h>
+#include <asm/page.h>
+#include <asm/processor-flags.h>
+#include <asm/msr-index.h>
+
+ .text
+ .code64
+ENTRY(sme_encrypt_execute)
+
+ /*
+ * Entry parameters:
+ * RDI - virtual address for the encrypted kernel mapping
+ * RSI - virtual address for the decrypted kernel mapping
+ * RDX - length of kernel
+ * RCX - virtual address of the encryption workarea, including:
+ * - stack page (PAGE_SIZE)
+ * - encryption routine page (PAGE_SIZE)
+ * - intermediate copy buffer (PMD_PAGE_SIZE)
+ * R8 - physcial address of the pagetables to use for encryption
+ */
+
+ push %rbp
+ push %r12
+
+ /* Set up a one page stack in the non-encrypted memory area */
+ movq %rsp, %rbp /* Save current stack pointer */
+ movq %rcx, %rax /* Workarea stack page */
+ movq %rax, %rsp /* Set new stack pointer */
+ addq $PAGE_SIZE, %rsp /* Stack grows from the bottom */
+ addq $PAGE_SIZE, %rax /* Workarea encryption routine */
+
+ movq %rdi, %r10 /* Encrypted kernel */
+ movq %rsi, %r11 /* Decrypted kernel */
+ movq %rdx, %r12 /* Kernel length */
+
+ /* Copy encryption routine into the workarea */
+ movq %rax, %rdi /* Workarea encryption routine */
+ leaq .Lenc_start(%rip), %rsi /* Encryption routine */
+ movq $(.Lenc_stop - .Lenc_start), %rcx /* Encryption routine length */
+ rep movsb
+
+ /* Setup registers for call */
+ movq %r10, %rdi /* Encrypted kernel */
+ movq %r11, %rsi /* Decrypted kernel */
+ movq %r8, %rdx /* Pagetables used for encryption */
+ movq %r12, %rcx /* Kernel length */
+ movq %rax, %r8 /* Workarea encryption routine */
+ addq $PAGE_SIZE, %r8 /* Workarea intermediate copy buffer */
+
+ call *%rax /* Call the encryption routine */
+
+ movq %rbp, %rsp /* Restore original stack pointer */
+
+ pop %r12
+ pop %rbp
+
+ ret
+ENDPROC(sme_encrypt_execute)
+
+.Lenc_start:
+ENTRY(sme_enc_routine)
+/*
+ * Routine used to encrypt kernel.
+ * This routine must be run outside of the kernel proper since
+ * the kernel will be encrypted during the process. So this
+ * routine is defined here and then copied to an area outside
+ * of the kernel where it will remain and run decrypted
+ * during execution.
+ *
+ * On entry the registers must be:
+ * RDI - virtual address for the encrypted kernel mapping
+ * RSI - virtual address for the decrypted kernel mapping
+ * RDX - address of the pagetables to use for encryption
+ * RCX - length of kernel
+ * R8 - intermediate copy buffer
+ *
+ * RAX - points to this routine
+ *
+ * The kernel will be encrypted by copying from the non-encrypted
+ * kernel space to an intermediate buffer and then copying from the
+ * intermediate buffer back to the encrypted kernel space. The physical
+ * addresses of the two kernel space mappings are the same which
+ * results in the kernel being encrypted "in place".
+ */
+ /* Enable the new page tables */
+ mov %rdx, %cr3
+
+ /* Flush any global TLBs */
+ mov %cr4, %rdx
+ andq $~X86_CR4_PGE, %rdx
+ mov %rdx, %cr4
+ orq $X86_CR4_PGE, %rdx
+ mov %rdx, %cr4
+
+ /* Set the PAT register PA5 entry to write-protect */
+ push %rcx
+ movl $MSR_IA32_CR_PAT, %ecx
+ rdmsr
+ push %rdx /* Save original PAT value */
+ andl $0xffff00ff, %edx /* Clear PA5 */
+ orl $0x00000500, %edx /* Set PA5 to WP */
+ wrmsr
+ pop %rdx /* RDX contains original PAT value */
+ pop %rcx
+
+ movq %rcx, %r9 /* Save kernel length */
+ movq %rdi, %r10 /* Save encrypted kernel address */
+ movq %rsi, %r11 /* Save decrypted kernel address */
+
+ wbinvd /* Invalidate any cache entries */
+
+ /* Copy/encrypt 2MB at a time */
+1:
+ movq %r11, %rsi /* Source - decrypted kernel */
+ movq %r8, %rdi /* Dest - intermediate copy buffer */
+ movq $PMD_PAGE_SIZE, %rcx /* 2MB length */
+ rep movsb
+
+ movq %r8, %rsi /* Source - intermediate copy buffer */
+ movq %r10, %rdi /* Dest - encrypted kernel */
+ movq $PMD_PAGE_SIZE, %rcx /* 2MB length */
+ rep movsb
+
+ addq $PMD_PAGE_SIZE, %r11
+ addq $PMD_PAGE_SIZE, %r10
+ subq $PMD_PAGE_SIZE, %r9 /* Kernel length decrement */
+ jnz 1b /* Kernel length not zero? */
+
+ /* Restore PAT register */
+ push %rdx /* Save original PAT value */
+ movl $MSR_IA32_CR_PAT, %ecx
+ rdmsr
+ pop %rdx /* Restore original PAT value */
+ wrmsr
+
+ ret
+ENDPROC(sme_enc_routine)