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linux-stable/arch/x86/include/asm/sev.h
Kevin Loughlin 4338e40da8 x86/sev: Skip ROM range scans and validation for SEV-SNP guests 
commit 0f4a1e8098 upstream.

SEV-SNP requires encrypted memory to be validated before access.
Because the ROM memory range is not part of the e820 table, it is not
pre-validated by the BIOS. Therefore, if a SEV-SNP guest kernel wishes
to access this range, the guest must first validate the range.

The current SEV-SNP code does indeed scan the ROM range during early
boot and thus attempts to validate the ROM range in probe_roms().
However, this behavior is neither sufficient nor necessary for the
following reasons:

* With regards to sufficiency, if EFI_CONFIG_TABLES are not enabled and
  CONFIG_DMI_SCAN_MACHINE_NON_EFI_FALLBACK is set, the kernel will
  attempt to access the memory at SMBIOS_ENTRY_POINT_SCAN_START (which
  falls in the ROM range) prior to validation.

  For example, Project Oak Stage 0 provides a minimal guest firmware
  that currently meets these configuration conditions, meaning guests
  booting atop Oak Stage 0 firmware encounter a problematic call chain
  during dmi_setup() -> dmi_scan_machine() that results in a crash
  during boot if SEV-SNP is enabled.

* With regards to necessity, SEV-SNP guests generally read garbage
  (which changes across boots) from the ROM range, meaning these scans
  are unnecessary. The guest reads garbage because the legacy ROM range
  is unencrypted data but is accessed via an encrypted PMD during early
  boot (where the PMD is marked as encrypted due to potentially mapping
  actually-encrypted data in other PMD-contained ranges).

In one exceptional case, EISA probing treats the ROM range as
unencrypted data, which is inconsistent with other probing.

Continuing to allow SEV-SNP guests to use garbage and to inconsistently
classify ROM range encryption status can trigger undesirable behavior.
For instance, if garbage bytes appear to be a valid signature, memory
may be unnecessarily reserved for the ROM range. Future code or other
use cases may result in more problematic (arbitrary) behavior that
should be avoided.

While one solution would be to overhaul the early PMD mapping to always
treat the ROM region of the PMD as unencrypted, SEV-SNP guests do not
currently rely on data from the ROM region during early boot (and even
if they did, they would be mostly relying on garbage data anyways).

As a simpler solution, skip the ROM range scans (and the otherwise-
necessary range validation) during SEV-SNP guest early boot. The
potential SEV-SNP guest crash due to lack of ROM range validation is
thus avoided by simply not accessing the ROM range.

In most cases, skip the scans by overriding problematic x86_init
functions during sme_early_init() to SNP-safe variants, which can be
likened to x86_init overrides done for other platforms (ex: Xen); such
overrides also avoid the spread of cc_platform_has() checks throughout
the tree.

In the exceptional EISA case, still use cc_platform_has() for the
simplest change, given (1) checks for guest type (ex: Xen domain status)
are already performed here, and (2) these checks occur in a subsys
initcall instead of an x86_init function.

  [ bp: Massage commit message, remove "we"s. ]

Fixes: 9704c07bf9 ("x86/kernel: Validate ROM memory before accessing when SEV-SNP is active")
Signed-off-by: Kevin Loughlin <kevinloughlin@google.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Cc: <stable@kernel.org>
Link: https://lore.kernel.org/r/20240313121546.2964854-1-kevinloughlin@google.com
Signed-off-by: Kevin Loughlin <kevinloughlin@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2024-04-03 15:29:03 +02:00

246 lines
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/* SPDX-License-Identifier: GPL-2.0 */
/*
* AMD Encrypted Register State Support
*
* Author: Joerg Roedel <jroedel@suse.de>
*/
#ifndef __ASM_ENCRYPTED_STATE_H
#define __ASM_ENCRYPTED_STATE_H
#include <linux/types.h>
#include <linux/sev-guest.h>
#include <asm/insn.h>
#include <asm/sev-common.h>
#include <asm/bootparam.h>
#include <asm/coco.h>
#define GHCB_PROTOCOL_MIN 1ULL
#define GHCB_PROTOCOL_MAX 2ULL
#define GHCB_DEFAULT_USAGE 0ULL
#define VMGEXIT() { asm volatile("rep; vmmcall\n\r"); }
enum es_result {
ES_OK, /* All good */
ES_UNSUPPORTED, /* Requested operation not supported */
ES_VMM_ERROR, /* Unexpected state from the VMM */
ES_DECODE_FAILED, /* Instruction decoding failed */
ES_EXCEPTION, /* Instruction caused exception */
ES_RETRY, /* Retry instruction emulation */
};
struct es_fault_info {
unsigned long vector;
unsigned long error_code;
unsigned long cr2;
};
struct pt_regs;
/* ES instruction emulation context */
struct es_em_ctxt {
struct pt_regs *regs;
struct insn insn;
struct es_fault_info fi;
};
/*
* AMD SEV Confidential computing blob structure. The structure is
* defined in OVMF UEFI firmware header:
* https://github.com/tianocore/edk2/blob/master/OvmfPkg/Include/Guid/ConfidentialComputingSevSnpBlob.h
*/
#define CC_BLOB_SEV_HDR_MAGIC 0x45444d41
struct cc_blob_sev_info {
u32 magic;
u16 version;
u16 reserved;
u64 secrets_phys;
u32 secrets_len;
u32 rsvd1;
u64 cpuid_phys;
u32 cpuid_len;
u32 rsvd2;
} __packed;
void do_vc_no_ghcb(struct pt_regs *regs, unsigned long exit_code);
static inline u64 lower_bits(u64 val, unsigned int bits)
{
u64 mask = (1ULL << bits) - 1;
return (val & mask);
}
struct real_mode_header;
enum stack_type;
/* Early IDT entry points for #VC handler */
extern void vc_no_ghcb(void);
extern void vc_boot_ghcb(void);
extern bool handle_vc_boot_ghcb(struct pt_regs *regs);
/* PVALIDATE return codes */
#define PVALIDATE_FAIL_SIZEMISMATCH 6
/* Software defined (when rFlags.CF = 1) */
#define PVALIDATE_FAIL_NOUPDATE 255
/* RMP page size */
#define RMP_PG_SIZE_4K 0
#define RMP_PG_SIZE_2M 1
#define RMPADJUST_VMSA_PAGE_BIT BIT(16)
/* SNP Guest message request */
struct snp_req_data {
unsigned long req_gpa;
unsigned long resp_gpa;
unsigned long data_gpa;
unsigned int data_npages;
};
struct sev_guest_platform_data {
u64 secrets_gpa;
};
/*
* The secrets page contains 96-bytes of reserved field that can be used by
* the guest OS. The guest OS uses the area to save the message sequence
* number for each VMPCK.
*
* See the GHCB spec section Secret page layout for the format for this area.
*/
struct secrets_os_area {
u32 msg_seqno_0;
u32 msg_seqno_1;
u32 msg_seqno_2;
u32 msg_seqno_3;
u64 ap_jump_table_pa;
u8 rsvd[40];
u8 guest_usage[32];
} __packed;
#define VMPCK_KEY_LEN 32
/* See the SNP spec version 0.9 for secrets page format */
struct snp_secrets_page_layout {
u32 version;
u32 imien : 1,
rsvd1 : 31;
u32 fms;
u32 rsvd2;
u8 gosvw[16];
u8 vmpck0[VMPCK_KEY_LEN];
u8 vmpck1[VMPCK_KEY_LEN];
u8 vmpck2[VMPCK_KEY_LEN];
u8 vmpck3[VMPCK_KEY_LEN];
struct secrets_os_area os_area;
u8 rsvd3[3840];
} __packed;
#ifdef CONFIG_AMD_MEM_ENCRYPT
extern void __sev_es_ist_enter(struct pt_regs *regs);
extern void __sev_es_ist_exit(void);
static __always_inline void sev_es_ist_enter(struct pt_regs *regs)
{
if (cc_vendor == CC_VENDOR_AMD &&
cc_platform_has(CC_ATTR_GUEST_STATE_ENCRYPT))
__sev_es_ist_enter(regs);
}
static __always_inline void sev_es_ist_exit(void)
{
if (cc_vendor == CC_VENDOR_AMD &&
cc_platform_has(CC_ATTR_GUEST_STATE_ENCRYPT))
__sev_es_ist_exit();
}
extern int sev_es_setup_ap_jump_table(struct real_mode_header *rmh);
extern void __sev_es_nmi_complete(void);
static __always_inline void sev_es_nmi_complete(void)
{
if (cc_vendor == CC_VENDOR_AMD &&
cc_platform_has(CC_ATTR_GUEST_STATE_ENCRYPT))
__sev_es_nmi_complete();
}
extern int __init sev_es_efi_map_ghcbs(pgd_t *pgd);
extern void sev_enable(struct boot_params *bp);
static inline int rmpadjust(unsigned long vaddr, bool rmp_psize, unsigned long attrs)
{
int rc;
/* "rmpadjust" mnemonic support in binutils 2.36 and newer */
asm volatile(".byte 0xF3,0x0F,0x01,0xFE\n\t"
: "=a"(rc)
: "a"(vaddr), "c"(rmp_psize), "d"(attrs)
: "memory", "cc");
return rc;
}
static inline int pvalidate(unsigned long vaddr, bool rmp_psize, bool validate)
{
bool no_rmpupdate;
int rc;
/* "pvalidate" mnemonic support in binutils 2.36 and newer */
asm volatile(".byte 0xF2, 0x0F, 0x01, 0xFF\n\t"
CC_SET(c)
: CC_OUT(c) (no_rmpupdate), "=a"(rc)
: "a"(vaddr), "c"(rmp_psize), "d"(validate)
: "memory", "cc");
if (no_rmpupdate)
return PVALIDATE_FAIL_NOUPDATE;
return rc;
}
struct snp_guest_request_ioctl;
void setup_ghcb(void);
void __init early_snp_set_memory_private(unsigned long vaddr, unsigned long paddr,
unsigned long npages);
void __init early_snp_set_memory_shared(unsigned long vaddr, unsigned long paddr,
unsigned long npages);
void snp_set_memory_shared(unsigned long vaddr, unsigned long npages);
void snp_set_memory_private(unsigned long vaddr, unsigned long npages);
void snp_set_wakeup_secondary_cpu(void);
bool snp_init(struct boot_params *bp);
void __init __noreturn snp_abort(void);
void snp_dmi_setup(void);
int snp_issue_guest_request(u64 exit_code, struct snp_req_data *input, struct snp_guest_request_ioctl *rio);
void snp_accept_memory(phys_addr_t start, phys_addr_t end);
u64 snp_get_unsupported_features(u64 status);
u64 sev_get_status(void);
#else
static inline void sev_es_ist_enter(struct pt_regs *regs) { }
static inline void sev_es_ist_exit(void) { }
static inline int sev_es_setup_ap_jump_table(struct real_mode_header *rmh) { return 0; }
static inline void sev_es_nmi_complete(void) { }
static inline int sev_es_efi_map_ghcbs(pgd_t *pgd) { return 0; }
static inline void sev_enable(struct boot_params *bp) { }
static inline int pvalidate(unsigned long vaddr, bool rmp_psize, bool validate) { return 0; }
static inline int rmpadjust(unsigned long vaddr, bool rmp_psize, unsigned long attrs) { return 0; }
static inline void setup_ghcb(void) { }
static inline void __init
early_snp_set_memory_private(unsigned long vaddr, unsigned long paddr, unsigned long npages) { }
static inline void __init
early_snp_set_memory_shared(unsigned long vaddr, unsigned long paddr, unsigned long npages) { }
static inline void snp_set_memory_shared(unsigned long vaddr, unsigned long npages) { }
static inline void snp_set_memory_private(unsigned long vaddr, unsigned long npages) { }
static inline void snp_set_wakeup_secondary_cpu(void) { }
static inline bool snp_init(struct boot_params *bp) { return false; }
static inline void snp_abort(void) { }
static inline void snp_dmi_setup(void) { }
static inline int snp_issue_guest_request(u64 exit_code, struct snp_req_data *input, struct snp_guest_request_ioctl *rio)
{
return -ENOTTY;
}
static inline void snp_accept_memory(phys_addr_t start, phys_addr_t end) { }
static inline u64 snp_get_unsupported_features(u64 status) { return 0; }
static inline u64 sev_get_status(void) { return 0; }
#endif
#endif
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