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Subject[PATCH v4 3/4] x86/mm: add .data..decrypted section to hold shared variables
Date
kvmclock defines few static variables which are shared with the
hypervisor during the kvmclock initialization.

When SEV is active, memory is encrypted with a guest-specific key, and
if guest OS wants to share the memory region with hypervisor then it must
clear the C-bit before sharing it. Currently, we use
kernel_physical_mapping_init() to split large pages before clearing the
C-bit on shared pages. But it fails when called from the kvmclock
initialization (mainly because memblock allocator is not ready that early
during boot).

Add a __decrypted section attribute which can be used when defining
such shared variable. The so-defined variables will be placed in the
.data..decrypted section. This section is mapped with C=0 early
during boot, we also ensure that the initialized values are updated
to match with C=0 (i.e perform an in-place decryption). The
.data..decrypted section is PMD-aligned and sized so that we avoid
the need to split the large pages when mapping the section.

The sme_encrypt_kernel() was used to perform the in-place encryption
of the Linux kernel and initrd when SME is active. The routine has been
enhanced to decrypt the .data..decrypted section for both SME and SEV
cases.

Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Cc: kvm@vger.kernel.org
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Borislav Petkov <bp@suse.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: linux-kernel@vger.kernel.org
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Sean Christopherson <sean.j.christopherson@intel.com>
Cc: kvm@vger.kernel.org
Cc: "Radim Krčmář" <rkrcmar@redhat.com>
---
arch/x86/include/asm/mem_encrypt.h | 6 +++
arch/x86/kernel/head64.c | 11 +++++
arch/x86/kernel/vmlinux.lds.S | 17 +++++++
arch/x86/mm/mem_encrypt_identity.c | 94 ++++++++++++++++++++++++++++++++------
4 files changed, 113 insertions(+), 15 deletions(-)

diff --git a/arch/x86/include/asm/mem_encrypt.h b/arch/x86/include/asm/mem_encrypt.h
index c064383..802b2eb 100644
--- a/arch/x86/include/asm/mem_encrypt.h
+++ b/arch/x86/include/asm/mem_encrypt.h
@@ -52,6 +52,8 @@ void __init mem_encrypt_init(void);
bool sme_active(void);
bool sev_active(void);

+#define __decrypted __attribute__((__section__(".data..decrypted")))
+
#else /* !CONFIG_AMD_MEM_ENCRYPT */

#define sme_me_mask 0ULL
@@ -77,6 +79,8 @@ early_set_memory_decrypted(unsigned long vaddr, unsigned long size) { return 0;
static inline int __init
early_set_memory_encrypted(unsigned long vaddr, unsigned long size) { return 0; }

+#define __decrypted
+
#endif /* CONFIG_AMD_MEM_ENCRYPT */

/*
@@ -88,6 +92,8 @@ early_set_memory_encrypted(unsigned long vaddr, unsigned long size) { return 0;
#define __sme_pa(x) (__pa(x) | sme_me_mask)
#define __sme_pa_nodebug(x) (__pa_nodebug(x) | sme_me_mask)

+extern char __start_data_decrypted[], __end_data_decrypted[];
+
#endif /* __ASSEMBLY__ */

#endif /* __X86_MEM_ENCRYPT_H__ */
diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c
index 8047379..af39d68 100644
--- a/arch/x86/kernel/head64.c
+++ b/arch/x86/kernel/head64.c
@@ -112,6 +112,7 @@ static bool __head check_la57_support(unsigned long physaddr)
unsigned long __head __startup_64(unsigned long physaddr,
struct boot_params *bp)
{
+ unsigned long vaddr, vaddr_end;
unsigned long load_delta, *p;
unsigned long pgtable_flags;
pgdval_t *pgd;
@@ -234,6 +235,16 @@ unsigned long __head __startup_64(unsigned long physaddr,
/* Encrypt the kernel and related (if SME is active) */
sme_encrypt_kernel(bp);

+ /* Clear the memory encryption mask from the .data..decrypted section. */
+ if (mem_encrypt_active()) {
+ vaddr = (unsigned long)__start_data_decrypted;
+ vaddr_end = (unsigned long)__end_data_decrypted;
+ for (; vaddr < vaddr_end; vaddr += PMD_SIZE) {
+ i = pmd_index(vaddr);
+ pmd[i] -= sme_get_me_mask();
+ }
+ }
+
/*
* Return the SME encryption mask (if SME is active) to be used as a
* modifier for the initial pgdir entry programmed into CR3.
diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
index 8bde0a4..78d3169 100644
--- a/arch/x86/kernel/vmlinux.lds.S
+++ b/arch/x86/kernel/vmlinux.lds.S
@@ -89,6 +89,21 @@ PHDRS {
note PT_NOTE FLAGS(0); /* ___ */
}

+/*
+ * This section contains data which will be mapped as decrypted. Memory
+ * encryption operates on a page basis. Make this section PMD-aligned
+ * to avoid spliting the pages while mapping the section early.
+ *
+ * Note: We use a separate section so that only this section gets
+ * decrypted to avoid exposing more than we wish.
+ */
+#define DATA_DECRYPTED \
+ . = ALIGN(PMD_SIZE); \
+ __start_data_decrypted = .; \
+ *(.data..decrypted); \
+ . = ALIGN(PMD_SIZE); \
+ __end_data_decrypted = .; \
+
SECTIONS
{
#ifdef CONFIG_X86_32
@@ -171,6 +186,8 @@ SECTIONS
/* rarely changed data like cpu maps */
READ_MOSTLY_DATA(INTERNODE_CACHE_BYTES)

+ DATA_DECRYPTED
+
/* End of data section */
_edata = .;
} :data
diff --git a/arch/x86/mm/mem_encrypt_identity.c b/arch/x86/mm/mem_encrypt_identity.c
index 7659e65..08e70ba 100644
--- a/arch/x86/mm/mem_encrypt_identity.c
+++ b/arch/x86/mm/mem_encrypt_identity.c
@@ -51,6 +51,8 @@
(_PAGE_PAT | _PAGE_PWT))

#define PMD_FLAGS_ENC (PMD_FLAGS_LARGE | _PAGE_ENC)
+#define PMD_FLAGS_ENC_WP ((PMD_FLAGS_ENC & ~_PAGE_CACHE_MASK) | \
+ (_PAGE_PAT | _PAGE_PWT))

#define PTE_FLAGS (__PAGE_KERNEL_EXEC & ~_PAGE_GLOBAL)

@@ -59,6 +61,8 @@
(_PAGE_PAT | _PAGE_PWT))

#define PTE_FLAGS_ENC (PTE_FLAGS | _PAGE_ENC)
+#define PTE_FLAGS_ENC_WP ((PTE_FLAGS_ENC & ~_PAGE_CACHE_MASK) | \
+ (_PAGE_PAT | _PAGE_PWT))

struct sme_populate_pgd_data {
void *pgtable_area;
@@ -231,6 +235,11 @@ static void __init sme_map_range_encrypted(struct sme_populate_pgd_data *ppd)
__sme_map_range(ppd, PMD_FLAGS_ENC, PTE_FLAGS_ENC);
}

+static void __init sme_map_range_encrypted_wp(struct sme_populate_pgd_data *ppd)
+{
+ __sme_map_range(ppd, PMD_FLAGS_ENC_WP, PTE_FLAGS_ENC_WP);
+}
+
static void __init sme_map_range_decrypted(struct sme_populate_pgd_data *ppd)
{
__sme_map_range(ppd, PMD_FLAGS_DEC, PTE_FLAGS_DEC);
@@ -378,7 +387,10 @@ static void __init build_workarea_map(struct boot_params *bp,
ppd->paddr = workarea_start;
ppd->vaddr = workarea_start;
ppd->vaddr_end = workarea_end;
- sme_map_range_decrypted(ppd);
+ if (sev_active())
+ sme_map_range_encrypted(ppd);
+ else
+ sme_map_range_decrypted(ppd);

/* Flush the TLB - no globals so cr3 is enough */
native_write_cr3(__native_read_cr3());
@@ -435,16 +447,27 @@ static void __init build_workarea_map(struct boot_params *bp,
sme_map_range_decrypted_wp(ppd);
}

- /* Add decrypted workarea mappings to both kernel mappings */
+ /*
+ * When SEV is active, kernel is already encrypted hence mapping
+ * the initial workarea_start as encrypted. When SME is active,
+ * the kernel is not encrypted hence add decrypted workarea
+ * mappings to both kernel mappings.
+ */
ppd->paddr = workarea_start;
ppd->vaddr = workarea_start;
ppd->vaddr_end = workarea_end;
- sme_map_range_decrypted(ppd);
+ if (sev_active())
+ sme_map_range_encrypted(ppd);
+ else
+ sme_map_range_decrypted(ppd);

ppd->paddr = workarea_start;
ppd->vaddr = workarea_start + decrypted_base;
ppd->vaddr_end = workarea_end + decrypted_base;
- sme_map_range_decrypted(ppd);
+ if (sev_active())
+ sme_map_range_encrypted(ppd);
+ else
+ sme_map_range_decrypted(ppd);

wa->kernel_start = kernel_start;
wa->kernel_end = kernel_end;
@@ -487,28 +510,69 @@ static void __init teardown_workarea_map(struct sme_workarea_data *wa,
native_write_cr3(__native_read_cr3());
}

+static void __init decrypt_shared_data(struct sme_workarea_data *wa,
+ struct sme_populate_pgd_data *ppd)
+{
+ unsigned long decrypted_start, decrypted_end, decrypted_len;
+
+ /* Physical addresses of decrypted data section */
+ decrypted_start = __pa_symbol(__start_data_decrypted);
+ decrypted_end = ALIGN(__pa_symbol(__end_data_decrypted), PMD_PAGE_SIZE);
+ decrypted_len = decrypted_end - decrypted_start;
+
+ if (!decrypted_len)
+ return;
+
+ /* Add decrypted mapping for the section (identity) */
+ ppd->paddr = decrypted_start;
+ ppd->vaddr = decrypted_start;
+ ppd->vaddr_end = decrypted_end;
+ sme_map_range_decrypted(ppd);
+
+ /* Add encrypted-wp mapping for the section (non-identity) */
+ ppd->paddr = decrypted_start;
+ ppd->vaddr = decrypted_start + wa->decrypted_base;
+ ppd->vaddr_end = decrypted_end + wa->decrypted_base;
+ sme_map_range_encrypted_wp(ppd);
+
+ /* Perform in-place decryption */
+ sme_encrypt_execute(decrypted_start,
+ decrypted_start + wa->decrypted_base,
+ decrypted_len, wa->workarea_start,
+ (unsigned long)ppd->pgd);
+
+ ppd->vaddr = decrypted_start + wa->decrypted_base;
+ ppd->vaddr_end = decrypted_end + wa->decrypted_base;
+ sme_clear_pgd(ppd);
+}
+
void __init sme_encrypt_kernel(struct boot_params *bp)
{
struct sme_populate_pgd_data ppd;
struct sme_workarea_data wa;

- if (!sme_active())
+ if (!mem_encrypt_active())
return;

build_workarea_map(bp, &wa, &ppd);

- /* When SEV is active, encrypt kernel and initrd */
- sme_encrypt_execute(wa.kernel_start,
- wa.kernel_start + wa.decrypted_base,
- wa.kernel_len, wa.workarea_start,
- (unsigned long)ppd.pgd);
-
- if (wa.initrd_len)
- sme_encrypt_execute(wa.initrd_start,
- wa.initrd_start + wa.decrypted_base,
- wa.initrd_len, wa.workarea_start,
+ /* When SME is active, encrypt kernel and initrd */
+ if (sme_active()) {
+ sme_encrypt_execute(wa.kernel_start,
+ wa.kernel_start + wa.decrypted_base,
+ wa.kernel_len, wa.workarea_start,
(unsigned long)ppd.pgd);

+ if (wa.initrd_len)
+ sme_encrypt_execute(wa.initrd_start,
+ wa.initrd_start + wa.decrypted_base,
+ wa.initrd_len, wa.workarea_start,
+ (unsigned long)ppd.pgd);
+ }
+
+ /* Decrypt the contents of .data..decrypted section */
+ decrypt_shared_data(&wa, &ppd);
+
teardown_workarea_map(&wa, &ppd);
}

--
2.7.4
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