From 69712baf249570a1419e75dc1a103a44e375b2cd Mon Sep 17 00:00:00 2001
From: "Borislav Petkov (AMD)" <bp@alien8.de>
Date: Fri, 11 Aug 2023 23:38:24 +0200
Subject: [PATCH] x86/CPU/AMD: Fix the DIV(0) initial fix attempt
commit f58d6fbcb7c848b7f2469be339bc571f2e9d245b upstream.
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
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
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 | 1 +
4 files changed, 3 insertions(+), 2 deletions(-)
diff --git a/arch/x86/include/asm/entry-common.h b/arch/x86/include/asm/entry-common.h
index 4a382fb6a9ef..5443851d3aa6 100644
--- a/arch/x86/include/asm/entry-common.h
+++ b/arch/x86/include/asm/entry-common.h
@@ -78,6 +78,7 @@ 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 7f351093cd94..2bc1c78a7cc5 100644
--- a/arch/x86/kernel/cpu/amd.c
+++ b/arch/x86/kernel/cpu/amd.c
@@ -1332,3 +1332,4 @@ 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 28f5cc0a9dec..98838b784524 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -198,8 +198,6 @@ 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 8544bca6b335..1616e39ddc3f 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -3376,6 +3376,7 @@ static void svm_flush_tlb_gva(struct kvm_vcpu *vcpu, gva_t gva)
static void svm_prepare_guest_switch(struct kvm_vcpu *vcpu)
{
+ amd_clear_divider();
}
static inline void sync_cr8_to_lapic(struct kvm_vcpu *vcpu)