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Sat, 27 Dec 2025 01:48:23 -0800 (PST) X-Google-Smtp-Source: AGHT+IEkXjh17Gc3ONEKcCfBrAFN2l31vqQQnRDnJ4MvwWALmJZ3e0OuL60yRySzT1bcRHFj+7oOcQ== X-Received: by 2002:a05:600c:3b9d:b0:459:db7b:988e with SMTP id 5b1f17b1804b1-47d19555e07mr344065015e9.13.1766828903017; Sat, 27 Dec 2025 01:48:23 -0800 (PST) From: Paolo Bonzini To: qemu-devel@nongnu.org Cc: Zhao Liu , Farrah Chen , Zide Chen , Xiaoyao Li , "Xin Li (Intel)" Subject: [PULL 085/153] i386/cpu: Save/restore SSP0 MSR for FRED Date: Sat, 27 Dec 2025 10:46:50 +0100 Message-ID: <20251227094759.35658-11-pbonzini@redhat.com> X-Mailer: git-send-email 2.52.0 In-Reply-To: <20251227091622.20725-1-pbonzini@redhat.com> References: <20251227091622.20725-1-pbonzini@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Received-SPF: pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists.gnu.org; Received-SPF: pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; 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charset="utf-8" From: "Xin Li (Intel)" Both FRED and CET shadow stack define the MSR MSR_IA32_PL0_SSP (aka MSR_IA32_FRED_SSP0 in FRED spec). MSR_IA32_PL0_SSP is a FRED SSP MSR, so that if a processor doesn't support CET shadow stack, FRED transitions won't use MSR_IA32_PL0_SSP, but this MSR would still be accessible using MSR-access instructions (e.g., RDMSR, WRMSR). Therefore, save/restore SSP0 MSR for FRED. Tested-by: Farrah Chen Signed-off-by: Xin Li (Intel) Signed-off-by: Zhao Liu Link: https://lore.kernel.org/r/20251211060801.3600039-14-zhao1.liu@intel.c= om Signed-off-by: Paolo Bonzini --- target/i386/cpu.h | 6 ++++++ target/i386/kvm/kvm.c | 13 +++++++++++++ 2 files changed, 19 insertions(+) diff --git a/target/i386/cpu.h b/target/i386/cpu.h index a1ff2ceb0c3..84e5cf0ab0c 100644 --- a/target/i386/cpu.h +++ b/target/i386/cpu.h @@ -554,6 +554,9 @@ typedef enum X86Seg { #define MSR_IA32_FRED_SSP3 0x000001d3 /* Stack level 3 = shadow stack pointer in ring 0 */ #define MSR_IA32_FRED_CONFIG 0x000001d4 /* FRED Entrypoin= t and interrupt stack level */ =20 +/* FRED and CET MSR */ +#define MSR_IA32_PL0_SSP 0x000006a4 /* ring-0 shadow = stack pointer (aka MSR_IA32_FRED_SSP0 for FRED) */ + #define MSR_IA32_BNDCFGS 0x00000d90 #define MSR_IA32_XSS 0x00000da0 #define MSR_IA32_UMWAIT_CONTROL 0xe1 @@ -1970,6 +1973,9 @@ typedef struct CPUArchState { uint64_t fred_config; #endif =20 + /* MSR used for both FRED and CET (SHSTK) */ + uint64_t pl0_ssp; + uint64_t tsc_adjust; uint64_t tsc_deadline; uint64_t tsc_aux; diff --git a/target/i386/kvm/kvm.c b/target/i386/kvm/kvm.c index e98da47a451..5b8c7550a16 100644 --- a/target/i386/kvm/kvm.c +++ b/target/i386/kvm/kvm.c @@ -4009,6 +4009,11 @@ static int kvm_put_msrs(X86CPU *cpu, KvmPutState lev= el) kvm_msr_entry_add(cpu, MSR_IA32_FRED_SSP2, env->fred_ssp2); kvm_msr_entry_add(cpu, MSR_IA32_FRED_SSP3, env->fred_ssp3); kvm_msr_entry_add(cpu, MSR_IA32_FRED_CONFIG, env->fred_config); + /* + * Aka MSR_IA32_FRED_SSP0. This MSR is accessible even if + * CET shadow stack is not supported. + */ + kvm_msr_entry_add(cpu, MSR_IA32_PL0_SSP, env->pl0_ssp); } } #endif @@ -4496,6 +4501,11 @@ static int kvm_get_msrs(X86CPU *cpu) kvm_msr_entry_add(cpu, MSR_IA32_FRED_SSP2, 0); kvm_msr_entry_add(cpu, MSR_IA32_FRED_SSP3, 0); kvm_msr_entry_add(cpu, MSR_IA32_FRED_CONFIG, 0); + /* + * Aka MSR_IA32_FRED_SSP0. This MSR is accessible even if + * CET shadow stack is not supported. + */ + kvm_msr_entry_add(cpu, MSR_IA32_PL0_SSP, 0); } } #endif @@ -4747,6 +4757,9 @@ static int kvm_get_msrs(X86CPU *cpu) case MSR_IA32_FRED_CONFIG: env->fred_config =3D msrs[i].data; break; + case MSR_IA32_PL0_SSP: /* aka MSR_IA32_FRED_SSP0 */ + env->pl0_ssp =3D msrs[i].data; + break; #endif case MSR_IA32_TSC: env->tsc =3D msrs[i].data; --=20 2.52.0