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

[Brijesh Singh]

On 09/14/2018 09:12 AM, Borislav Petkov wrote:

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();
+       }
  }

The above code will never get executed for the SEV case.

See if (!sme_active()) check in the start of function.

If we decide to go on this patch, then we have to do something like
this:

sme_encrypt_kernel(...)
{
        if (!mem_encrypt_active())
                return;

        if (sev_active())
                goto out;

        /* Do kernel and initrd in-place encrypts for SME only case */
        .....
        .....

out:
        /* Clear the C-bit from .bss..decrypted section */
        ...
        ...
}

void __init sme_enable(struct boot_params *bp)