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Commit b3f0907c authored by Brijesh Singh's avatar Brijesh Singh Committed by Thomas Gleixner
Browse files

x86/mm: Add .bss..decrypted section to hold shared variables 



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 the guest OS wants to share the memory region with the 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 the memblock allocator is
not ready that early during boot).

Add a __bss_decrypted section attribute which can be used when defining
such shared variable. The so-defined variables will be placed in the
.bss..decrypted section. This section will be mapped with C=0 early
during boot.

The .bss..decrypted section has a big chunk of memory that may be unused
when memory encryption is not active, free it when memory encryption is
not active.

Suggested-by: default avatarThomas Gleixner <tglx@linutronix.de>
Signed-off-by: default avatarBrijesh Singh <brijesh.singh@amd.com>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Cc: Borislav Petkov <bp@suse.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Sean Christopherson <sean.j.christopherson@intel.com>
Cc: Radim Krčmář<rkrcmar@redhat.com>
Cc: kvm@vger.kernel.org
Link: https://lkml.kernel.org/r/1536932759-12905-2-git-send-email-brijesh.singh@amd.com
parent 27c5a778

arch/x86/include/asm/mem_encrypt.h

+7 −0
Original line number Diff line number Diff line
@@ -48,10 +48,13 @@ int __init early_set_memory_encrypted(unsigned long vaddr, unsigned long size); 


/* Architecture __weak replacement functions */

void __init mem_encrypt_init(void);

void __init mem_encrypt_free_decrypted_mem(void);



bool sme_active(void);

bool sev_active(void);



#define __bss_decrypted __attribute__((__section__(".bss..decrypted")))



#else	/* !CONFIG_AMD_MEM_ENCRYPT */



#define sme_me_mask	0ULL
@@ -77,6 +80,8 @@ 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 __bss_decrypted



#endif	/* CONFIG_AMD_MEM_ENCRYPT */



/*
@@ -88,6 +93,8 @@ 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_bss_decrypted[], __end_bss_decrypted[], __start_bss_decrypted_unused[];



#endif	/* __ASSEMBLY__ */



#endif	/* __X86_MEM_ENCRYPT_H__ */

arch/x86/kernel/head64.c

+16 −0
Original line number Diff line number Diff line
@@ -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 +235,21 @@ 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 .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();

		}

	}



	/*

	 * Return the SME encryption mask (if SME is active) to be used as a

	 * modifier for the initial pgdir entry programmed into CR3.

arch/x86/kernel/vmlinux.lds.S

+19 −0
Original line number Diff line number Diff line
@@ -65,6 +65,23 @@ jiffies_64 = jiffies; 
#define ALIGN_ENTRY_TEXT_BEGIN	. = ALIGN(PMD_SIZE);

#define ALIGN_ENTRY_TEXT_END	. = ALIGN(PMD_SIZE);



/*

 * This section contains data which will be mapped as decrypted. Memory

 * encryption operates on a page basis. Make this section PMD-aligned

 * to avoid splitting 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 BSS_DECRYPTED						\

	. = ALIGN(PMD_SIZE);					\

	__start_bss_decrypted = .;				\

	*(.bss..decrypted);					\

	. = ALIGN(PAGE_SIZE);					\

	__start_bss_decrypted_unused = .;			\

	. = ALIGN(PMD_SIZE);					\

	__end_bss_decrypted = .;				\



#else



#define X86_ALIGN_RODATA_BEGIN
@@ -74,6 +91,7 @@ jiffies_64 = jiffies; 


#define ALIGN_ENTRY_TEXT_BEGIN

#define ALIGN_ENTRY_TEXT_END

#define BSS_DECRYPTED



#endif
@@ -355,6 +373,7 @@ SECTIONS 
		__bss_start = .;

		*(.bss..page_aligned)

		*(.bss)

		BSS_DECRYPTED

		. = ALIGN(PAGE_SIZE);

		__bss_stop = .;

	}

arch/x86/mm/init.c

+4 −0
Original line number Diff line number Diff line
@@ -815,10 +815,14 @@ void free_kernel_image_pages(void *begin, void *end) 
		set_memory_np_noalias(begin_ul, len_pages);

}



void __weak mem_encrypt_free_decrypted_mem(void) { }



void __ref free_initmem(void)

{

	e820__reallocate_tables();



	mem_encrypt_free_decrypted_mem();



	free_kernel_image_pages(&__init_begin, &__init_end);

}

arch/x86/mm/mem_encrypt.c

+24 −0
Original line number Diff line number Diff line
@@ -348,6 +348,30 @@ bool sev_active(void) 
EXPORT_SYMBOL(sev_active);



/* Architecture __weak replacement functions */

void __init mem_encrypt_free_decrypted_mem(void)

{

	unsigned long vaddr, vaddr_end, npages;

	int r;



	vaddr = (unsigned long)__start_bss_decrypted_unused;

	vaddr_end = (unsigned long)__end_bss_decrypted;

	npages = (vaddr_end - vaddr) >> PAGE_SHIFT;



	/*

	 * The unused memory range was mapped decrypted, change the encryption

	 * attribute from decrypted to encrypted before freeing it.

	 */

	if (mem_encrypt_active()) {

		r = set_memory_encrypted(vaddr, npages);

		if (r) {

			pr_warn("failed to free unused decrypted pages\n");

			return;

		}

	}



	free_init_pages("unused decrypted", vaddr, vaddr_end);

}



void __init mem_encrypt_init(void)

{

	if (!sme_me_mask)