diff mbox series

[SRU,OEM-6.1,Lunar,3/3] x86/CPU/AMD: Fix the DIV(0) initial fix attempt

Message ID 20230830143837.220465-10-cascardo@canonical.com
State New
Headers show
Series None | expand

Commit Message

Thadeu Lima de Souza Cascardo Aug. 30, 2023, 2:38 p.m. UTC 
From: "Borislav Petkov (AMD)" <bp@alien8.de>

Initially, it was thought that doing an innocuous division in the #DE
handler would take care to prevent any leaking of old data from the
divider but by the time the fault is raised, the speculation has already
advanced too far and such data could already have been used by younger
operations.

Therefore, do the innocuous division on every exit to userspace so that
userspace doesn't see any potentially old data from integer divisions in
kernel space.

Do the same before VMRUN too, to protect host data from leaking into the
guest too.

Fixes: 77245f1c3c64 ("x86/CPU/AMD: Do not leak quotient data after a division by 0")
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Cc: <stable@kernel.org>
Link: https://lore.kernel.org/r/20230811213824.10025-1-bp@alien8.de
(cherry picked from commit f58d6fbcb7c848b7f2469be339bc571f2e9d245b)
CVE-2023-20588
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>
---
 arch/x86/include/asm/entry-common.h | 1 +
 arch/x86/kernel/cpu/amd.c           | 1 +
 arch/x86/kernel/traps.c             | 2 --
 arch/x86/kvm/svm/svm.c              | 2 ++
 4 files changed, 4 insertions(+), 2 deletions(-)
diff mbox series

Patch

diff --git a/arch/x86/include/asm/entry-common.h b/arch/x86/include/asm/entry-common.h
index 117903881fe4..ce8f50192ae3 100644
--- a/arch/x86/include/asm/entry-common.h
+++ b/arch/x86/include/asm/entry-common.h
@@ -92,6 +92,7 @@  static inline void arch_exit_to_user_mode_prepare(struct pt_regs *regs,
 static __always_inline void arch_exit_to_user_mode(void)
 {
 	mds_user_clear_cpu_buffers();
+	amd_clear_divider();
 }
 #define arch_exit_to_user_mode arch_exit_to_user_mode
 
diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
index fe22188dd1b9..e857be4f7818 100644
--- a/arch/x86/kernel/cpu/amd.c
+++ b/arch/x86/kernel/cpu/amd.c
@@ -1275,3 +1275,4 @@  void noinstr amd_clear_divider(void)
 	asm volatile(ALTERNATIVE("", "div %2\n\t", X86_BUG_DIV0)
 		     :: "a" (0), "d" (0), "r" (1));
 }
+EXPORT_SYMBOL_GPL(amd_clear_divider);
diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index 9437cadca9a0..d317dc3d06a3 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -206,8 +206,6 @@  DEFINE_IDTENTRY(exc_divide_error)
 {
 	do_error_trap(regs, 0, "divide error", X86_TRAP_DE, SIGFPE,
 		      FPE_INTDIV, error_get_trap_addr(regs));
-
-	amd_clear_divider();
 }
 
 DEFINE_IDTENTRY(exc_overflow)
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index a682ca4c9fe1..51cdd364b7af 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -3945,6 +3945,8 @@  static noinstr void svm_vcpu_enter_exit(struct kvm_vcpu *vcpu, bool spec_ctrl_in
 
 	guest_state_enter_irqoff();
 
+	amd_clear_divider();
+
 	if (sev_es_guest(vcpu->kvm))
 		__svm_sev_es_vcpu_run(svm, spec_ctrl_intercepted);
 	else