From ad4e22de3379871b018233e80c6ac41ba4acc0e9 Mon Sep 17 00:00:00 2001 From: "Borislav Petkov (AMD)" 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) Cc: Link: https://lore.kernel.org/r/20230811213824.10025-1-bp@alien8.de Signed-off-by: Greg Kroah-Hartman --- 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 --git a/arch/x86/include/asm/entry-common.h b/arch/x86/include/asm/entry-common.h index 43184640b579..a12fdf01dc26 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 0ca7123417ab..0a0230bd5089 100644 --- a/arch/x86/kernel/cpu/amd.c +++ b/arch/x86/kernel/cpu/amd.c @@ -1320,3 +1320,4 @@ 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 3361d32d090f..ca47080e3774 100644 --- a/arch/x86/kernel/traps.c +++ b/arch/x86/kernel/traps.c @@ -202,8 +202,6 @@ 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 d63c3843e493..8e9a6c41f9ee 100644 --- a/arch/x86/kvm/svm/svm.c +++ b/arch/x86/kvm/svm/svm.c @@ -1452,6 +1452,8 @@ static void svm_prepare_guest_switch(struct kvm_vcpu *vcpu) struct vcpu_svm *svm = to_svm(vcpu); struct svm_cpu_data *sd = per_cpu(svm_data, vcpu->cpu); + amd_clear_divider(); + if (sev_es_guest(vcpu->kvm)) sev_es_unmap_ghcb(svm);