From: Borislav Petkov (AMD) <bp@xxxxxxxxx>
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@xxxxxxxxx>
Cc: <stable@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20230811213824.10025-1-bp@xxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
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(-)
--- 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_mod
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
--- a/arch/x86/kernel/cpu/amd.c
+++ b/arch/x86/kernel/cpu/amd.c
@@ -1331,3 +1331,4 @@ 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);
--- 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)
--- 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
static void svm_prepare_guest_switch(struct kvm_vcpu *vcpu)
{
+ amd_clear_divider();
}
static inline void sync_cr8_to_lapic(struct kvm_vcpu *vcpu)
