From: Igor Druzhinin Date: Thu, 27 Jun 2019 19:41:54 +0000 (+0100) Subject: x86/cpuid: leak OSXSAVE only when XSAVE is not clear in policy X-Git-Tag: archive/raspbian/4.14.0+80-gd101b417b7-1+rpi1^2~63^2~1974 X-Git-Url: https://dgit.raspbian.org/?a=commitdiff_plain;h=902888922e6feda2c485cc4bdeffd0d6e6c26e14;p=xen.git x86/cpuid: leak OSXSAVE only when XSAVE is not clear in policy This fixes booting of old non-PV-OPS kernels which historically looked for OSXSAVE instead of XSAVE bit in CPUID to check whether XSAVE feature is enabled. If such a guest appears to be started on an XSAVE enabled CPU and the feature is explicitly cleared in policy, leaked OSXSAVE bit from Xen will lead to guest crash early in boot. Signed-off-by: Igor Druzhinin Reviewed-by: Andrew Cooper --- diff --git a/xen/arch/x86/cpuid.c b/xen/arch/x86/cpuid.c index ea9bfc51b6..ab1a48ff90 100644 --- a/xen/arch/x86/cpuid.c +++ b/xen/arch/x86/cpuid.c @@ -770,7 +770,8 @@ void guest_cpuid(const struct vcpu *v, uint32_t leaf, * damage itself. * * - Enlightened CPUID or CPUID faulting available: - * Xen can fully control what is seen here. Guest kernels need + * Xen can fully control what is seen here. When the guest has + * been configured to have XSAVE available, guest kernels need * to see the leaked OSXSAVE via the enlightened path, but * guest userspace and the native is given architectural * behaviour. @@ -780,7 +781,8 @@ void guest_cpuid(const struct vcpu *v, uint32_t leaf, */ /* OSXSAVE clear in policy. Fast-forward CR4 back in. */ if ( (v->arch.pv.ctrlreg[4] & X86_CR4_OSXSAVE) || - (regs->entry_vector == TRAP_invalid_op && + (p->basic.xsave && + regs->entry_vector == TRAP_invalid_op && guest_kernel_mode(v, regs) && (read_cr4() & X86_CR4_OSXSAVE)) ) res->c |= cpufeat_mask(X86_FEATURE_OSXSAVE);