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x86/sev: Move MSR-based VMGEXITs for CPUID to helper

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This code will also be used later for SEV-SNP-validated CPUID code in
some cases, so move it to a common helper.

While here, also add a check to terminate in cases where the CPUID
function/subfunction is indexed and the subfunction is non-zero, since
the GHCB MSR protocol does not support non-zero subfunctions.

Suggested-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Michael Roth <michael.roth@amd.com>
Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lore.kernel.org/r/20220307213356.2797205-32-brijesh.singh@amd.com
This commit is contained in:
Michael Roth 2022-02-24 10:56:11 -06:00 committed by Borislav Petkov
parent b66370db9a
commit 801baa693c
3 changed files with 59 additions and 26 deletions
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1
arch/x86/boot/compressed/sev.c
View file

@ -20,6 +20,7 @@
#include <asm/fpu/xcr.h>
#include <asm/ptrace.h>
#include <asm/svm.h>
#include <asm/cpuid.h>
#include "error.h"
#include "../msr.h"

83
arch/x86/kernel/sev-shared.c
View file

@ -14,6 +14,16 @@
#define has_cpuflag(f) boot_cpu_has(f)
#endif
/* I/O parameters for CPUID-related helpers */
struct cpuid_leaf {
u32 fn;
u32 subfn;
u32 eax;
u32 ebx;
u32 ecx;
u32 edx;
};
/*
* Since feature negotiation related variables are set early in the boot
* process they must reside in the .data section so as not to be zeroed
@ -194,6 +204,44 @@ enum es_result sev_es_ghcb_hv_call(struct ghcb *ghcb, bool set_ghcb_msr,
return verify_exception_info(ghcb, ctxt);
}
static int __sev_cpuid_hv(u32 fn, int reg_idx, u32 *reg)
{
u64 val;
sev_es_wr_ghcb_msr(GHCB_CPUID_REQ(fn, reg_idx));
VMGEXIT();
val = sev_es_rd_ghcb_msr();
if (GHCB_RESP_CODE(val) != GHCB_MSR_CPUID_RESP)
return -EIO;
*reg = (val >> 32);
return 0;
}
static int sev_cpuid_hv(struct cpuid_leaf *leaf)
{
int ret;
/*
* MSR protocol does not support fetching non-zero subfunctions, but is
* sufficient to handle current early-boot cases. Should that change,
* make sure to report an error rather than ignoring the index and
* grabbing random values. If this issue arises in the future, handling
* can be added here to use GHCB-page protocol for cases that occur late
* enough in boot that GHCB page is available.
*/
if (cpuid_function_is_indexed(leaf->fn) && leaf->subfn)
return -EINVAL;
ret = __sev_cpuid_hv(leaf->fn, GHCB_CPUID_REQ_EAX, &leaf->eax);
ret = ret ? : __sev_cpuid_hv(leaf->fn, GHCB_CPUID_REQ_EBX, &leaf->ebx);
ret = ret ? : __sev_cpuid_hv(leaf->fn, GHCB_CPUID_REQ_ECX, &leaf->ecx);
ret = ret ? : __sev_cpuid_hv(leaf->fn, GHCB_CPUID_REQ_EDX, &leaf->edx);
return ret;
}
/*
* Boot VC Handler - This is the first VC handler during boot, there is no GHCB
* page yet, so it only supports the MSR based communication with the
@ -201,40 +249,23 @@ enum es_result sev_es_ghcb_hv_call(struct ghcb *ghcb, bool set_ghcb_msr,
*/
void __init do_vc_no_ghcb(struct pt_regs *regs, unsigned long exit_code)
{
unsigned int subfn = lower_bits(regs->cx, 32);
unsigned int fn = lower_bits(regs->ax, 32);
unsigned long val;
struct cpuid_leaf leaf;
/* Only CPUID is supported via MSR protocol */
if (exit_code != SVM_EXIT_CPUID)
goto fail;
sev_es_wr_ghcb_msr(GHCB_CPUID_REQ(fn, GHCB_CPUID_REQ_EAX));
VMGEXIT();
val = sev_es_rd_ghcb_msr();
if (GHCB_RESP_CODE(val) != GHCB_MSR_CPUID_RESP)
leaf.fn = fn;
leaf.subfn = subfn;
if (sev_cpuid_hv(&leaf))
goto fail;
regs->ax = val >> 32;
sev_es_wr_ghcb_msr(GHCB_CPUID_REQ(fn, GHCB_CPUID_REQ_EBX));
VMGEXIT();
val = sev_es_rd_ghcb_msr();
if (GHCB_RESP_CODE(val) != GHCB_MSR_CPUID_RESP)
goto fail;
regs->bx = val >> 32;
sev_es_wr_ghcb_msr(GHCB_CPUID_REQ(fn, GHCB_CPUID_REQ_ECX));
VMGEXIT();
val = sev_es_rd_ghcb_msr();
if (GHCB_RESP_CODE(val) != GHCB_MSR_CPUID_RESP)
goto fail;
regs->cx = val >> 32;
sev_es_wr_ghcb_msr(GHCB_CPUID_REQ(fn, GHCB_CPUID_REQ_EDX));
VMGEXIT();
val = sev_es_rd_ghcb_msr();
if (GHCB_RESP_CODE(val) != GHCB_MSR_CPUID_RESP)
goto fail;
regs->dx = val >> 32;
regs->ax = leaf.eax;
regs->bx = leaf.ebx;
regs->cx = leaf.ecx;
regs->dx = leaf.edx;
/*
* This is a VC handler and the #VC is only raised when SEV-ES is

1
arch/x86/kernel/sev.c
View file

@ -33,6 +33,7 @@
#include <asm/smp.h>
#include <asm/cpu.h>
#include <asm/apic.h>
#include <asm/cpuid.h>
#define DR7_RESET_VALUE 0x400