Commit 541ac971 authored by Borislav Petkov's avatar Borislav Petkov
Browse files

x86/sev: Make the #VC exception stacks part of the default stacks storage 



The size of the exception stacks was increased by the commit in Fixes,
resulting in stack sizes greater than a page in size. The #VC exception
handling was only mapping the first (bottom) page, resulting in an
SEV-ES guest failing to boot.

Make the #VC exception stacks part of the default exception stacks
storage and allocate them with a CONFIG_AMD_MEM_ENCRYPT=y .config. Map
them only when a SEV-ES guest has been detected.

Rip out the custom VC stacks mapping and storage code.

 [ bp: Steal and adapt Tom's commit message. ]

Fixes: 7fae4c24 ("x86: Increase exception stack sizes")
Signed-off-by: default avatarBorislav Petkov <bp@suse.de>
Tested-by: default avatarTom Lendacky <thomas.lendacky@amd.com>
Tested-by: default avatarBrijesh Singh <brijesh.singh@amd.com>
Link: https://lkml.kernel.org/r/YVt1IMjIs7pIZTRR@zn.tnic
parent c7419a6e

arch/x86/include/asm/cpu_entry_area.h

+7 −1
Original line number Diff line number Diff line
@@ -10,6 +10,12 @@ 


#ifdef CONFIG_X86_64



#ifdef CONFIG_AMD_MEM_ENCRYPT

#define VC_EXCEPTION_STKSZ	EXCEPTION_STKSZ

#else

#define VC_EXCEPTION_STKSZ	0

#endif



/* Macro to enforce the same ordering and stack sizes */

#define ESTACKS_MEMBERS(guardsize, optional_stack_size)		\

	char	DF_stack_guard[guardsize];			\
@@ -28,7 +34,7 @@ 


/* The exception stacks' physical storage. No guard pages required */

struct exception_stacks {

	ESTACKS_MEMBERS(0, 0)

	ESTACKS_MEMBERS(0, VC_EXCEPTION_STKSZ)

};



/* The effective cpu entry area mapping with guard pages. */

arch/x86/kernel/sev.c

+0 −32
Original line number Diff line number Diff line
@@ -46,16 +46,6 @@ static struct ghcb __initdata *boot_ghcb; 
struct sev_es_runtime_data {

	struct ghcb ghcb_page;



	/* Physical storage for the per-CPU IST stack of the #VC handler */

	char ist_stack[EXCEPTION_STKSZ] __aligned(PAGE_SIZE);



	/*

	 * Physical storage for the per-CPU fall-back stack of the #VC handler.

	 * The fall-back stack is used when it is not safe to switch back to the

	 * interrupted stack in the #VC entry code.

	 */

	char fallback_stack[EXCEPTION_STKSZ] __aligned(PAGE_SIZE);



	/*

	 * Reserve one page per CPU as backup storage for the unencrypted GHCB.

	 * It is needed when an NMI happens while the #VC handler uses the real
@@ -99,27 +89,6 @@ DEFINE_STATIC_KEY_FALSE(sev_es_enable_key); 
/* Needed in vc_early_forward_exception */

void do_early_exception(struct pt_regs *regs, int trapnr);



static void __init setup_vc_stacks(int cpu)

{

	struct sev_es_runtime_data *data;

	struct cpu_entry_area *cea;

	unsigned long vaddr;

	phys_addr_t pa;



	data = per_cpu(runtime_data, cpu);

	cea  = get_cpu_entry_area(cpu);



	/* Map #VC IST stack */

	vaddr = CEA_ESTACK_BOT(&cea->estacks, VC);

	pa    = __pa(data->ist_stack);

	cea_set_pte((void *)vaddr, pa, PAGE_KERNEL);



	/* Map VC fall-back stack */

	vaddr = CEA_ESTACK_BOT(&cea->estacks, VC2);

	pa    = __pa(data->fallback_stack);

	cea_set_pte((void *)vaddr, pa, PAGE_KERNEL);

}



static __always_inline bool on_vc_stack(struct pt_regs *regs)

{

	unsigned long sp = regs->sp;
@@ -787,7 +756,6 @@ void __init sev_es_init_vc_handling(void) 
	for_each_possible_cpu(cpu) {

		alloc_runtime_data(cpu);

		init_ghcb(cpu);

		setup_vc_stacks(cpu);

	}



	sev_es_setup_play_dead();

arch/x86/mm/cpu_entry_area.c

+7 −0
Original line number Diff line number Diff line
@@ -110,6 +110,13 @@ static void __init percpu_setup_exception_stacks(unsigned int cpu) 
	cea_map_stack(NMI);

	cea_map_stack(DB);

	cea_map_stack(MCE);



	if (IS_ENABLED(CONFIG_AMD_MEM_ENCRYPT)) {

		if (cc_platform_has(CC_ATTR_GUEST_STATE_ENCRYPT)) {

			cea_map_stack(VC);

			cea_map_stack(VC2);

		}

	}

}

#else

static inline void percpu_setup_exception_stacks(unsigned int cpu)