Re: [PATCH v8 1/2] x86/mm: add .bss..decrypted section to hold shared variables

Borislav Petkov
2018-09-14T14:12:28Z

On Fri, Sep 14, 2018 at 02:17:05PM +0200, Thomas Gleixner wrote:
> > The sme_encrypt_kernel() does not have access to pmd (after pointer
> > fixup is applied). You can extend the sme_encrypt_kernel() to pass an
> > additional arguments but then we start getting in include hell. The pmd
> > is defined as "pmdval_t". If we extend the sme_encrypt_kernel() then
> > asm/mem_encrypt.h need to include the header file which defines
> > "pmdval_t". Adding the 'asm/pgtable_type.h' was causing all kind of
> > compilation errors. I didn't spend much time on it. IMO, we really don't
> > need to go in this path unless we see some value from doing this.
>
> Keep it here then.

*For what is worth*, a simple forward declaration works. I've taken the
64-bit forward declaration of pmdval_t as SME is 64-bit only anyway.

The below diff ontop passes the mandatory all*config smoke builds:

---
arch/x86/include/asm/mem_encrypt.h | 6 ++++--
arch/x86/kernel/head64.c | 18 +-----------------
arch/x86/mm/mem_encrypt_identity.c | 18 +++++++++++++++++-
3 files changed, 22 insertions(+), 20 deletions(-)

diff --git a/arch/x86/include/asm/mem_encrypt.h b/arch/x86/include/asm/mem_encrypt.h
index 616f8e637bc3..67c0e6cfdfb3 100644
--- a/arch/x86/include/asm/mem_encrypt.h
+++ b/arch/x86/include/asm/mem_encrypt.h
@@ -19,6 +19,8 @@

#include <asm/bootparam.h>

+typedef unsigned long pmdval_t;
+
#ifdef CONFIG_AMD_MEM_ENCRYPT

extern u64 sme_me_mask;
@@ -40,7 +42,7 @@ void __init sme_unmap_bootdata(char *real_mode_data);

void __init sme_early_init(void);

-void __init sme_encrypt_kernel(struct boot_params *bp);
+void __init sme_encrypt_kernel(struct boot_params *bp, pmdval_t *pmd);
void __init sme_enable(struct boot_params *bp);

int __init early_set_memory_decrypted(unsigned long vaddr, unsigned long size);
@@ -69,7 +71,7 @@ static inline void __init sme_unmap_bootdata(char *real_mode_data) { }

static inline void __init sme_early_init(void) { }

-static inline void __init sme_encrypt_kernel(struct boot_params *bp) { }
+static inline void __init sme_encrypt_kernel(struct boot_params *bp, pmdval_t *pmd) { }
static inline void __init sme_enable(struct boot_params *bp) { }

static inline bool sme_active(void) { return false; }
diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c
index c16af27eb23f..6f8e9b534e80 100644
--- a/arch/x86/kernel/head64.c
+++ b/arch/x86/kernel/head64.c
@@ -112,7 +112,6 @@ 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;
@@ -233,22 +232,7 @@ unsigned long __head __startup_64(unsigned long physaddr,
*fixup_long(&phys_base, physaddr) += load_delta - sme_get_me_mask();

/* Encrypt the kernel and related (if SME is active) */
- sme_encrypt_kernel(bp);
-
- /*
- * Clear the memory encryption mask from the .bss..decrypted section.
- * The bss section will be memset to zero later in the initialization so
- * there is no need to zero it after changing the memory encryption
- * attribute.
- */
- if (mem_encrypt_active()) {
- vaddr = (unsigned long)__start_bss_decrypted;
- vaddr_end = (unsigned long)__end_bss_decrypted;
- for (; vaddr < vaddr_end; vaddr += PMD_SIZE) {
- i = pmd_index(vaddr);
- pmd[i] -= sme_get_me_mask();
- }
- }
+ sme_encrypt_kernel(bp, pmd);

/*
* Return the SME encryption mask (if SME is active) to be used as a
diff --git a/arch/x86/mm/mem_encrypt_identity.c b/arch/x86/mm/mem_encrypt_identity.c
index a19ef1a416ff..9dbc145d10f8 100644
--- a/arch/x86/mm/mem_encrypt_identity.c
+++ b/arch/x86/mm/mem_encrypt_identity.c
@@ -267,15 +267,17 @@ static unsigned long __init sme_pgtable_calc(unsigned long len)
return entries + tables;
}

-void __init sme_encrypt_kernel(struct boot_params *bp)
+void __init sme_encrypt_kernel(struct boot_params *bp, pmdval_t *pmd)
{
unsigned long workarea_start, workarea_end, workarea_len;
unsigned long execute_start, execute_end, execute_len;
unsigned long kernel_start, kernel_end, kernel_len;
unsigned long initrd_start, initrd_end, initrd_len;
struct sme_populate_pgd_data ppd;
+ unsigned long vaddr, vaddr_end;
unsigned long pgtable_area_len;
unsigned long decrypted_base;
+ int i;

if (!sme_active())
return;
@@ -467,6 +469,20 @@ void __init sme_encrypt_kernel(struct boot_params *bp)

/* Flush the TLB - no globals so cr3 is enough */
native_write_cr3(__native_read_cr3());
+
+ /*
+ * Clear the memory encryption mask from the .bss..decrypted section.
+ * The bss section will be memset to zero later in the initialization so
+ * there is no need to zero it after changing the memory encryption
+ * attribute.
+ */
+ vaddr = (unsigned long)__start_bss_decrypted;
+ vaddr_end = (unsigned long)__end_bss_decrypted;
+
+ for (; vaddr < vaddr_end; vaddr += PMD_SIZE) {
+ i = pmd_index(vaddr);
+ pmd[i] -= sme_get_me_mask();
+ }
}

void __init sme_enable(struct boot_params *bp)
--
2.17.0.582.gccdcbd54c

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