From b4845bb6383821a9516ce30af3a27dc873e37fd4 Mon Sep 17 00:00:00 2001 From: Juergen Gross Date: Thu, 17 Oct 2024 11:00:52 +0200 Subject: x86/xen: add central hypercall functions Add generic hypercall functions usable for all normal (i.e. not iret) hypercalls. Depending on the guest type and the processor vendor different functions need to be used due to the to be used instruction for entering the hypervisor: - PV guests need to use syscall - HVM/PVH guests on Intel need to use vmcall - HVM/PVH guests on AMD and Hygon need to use vmmcall As PVH guests need to issue hypercalls very early during boot, there is a 4th hypercall function needed for HVM/PVH which can be used on Intel and AMD processors. It will check the vendor type and then set the Intel or AMD specific function to use via static_call(). This is part of XSA-466 / CVE-2024-53241. Reported-by: Andrew Cooper Signed-off-by: Juergen Gross Co-developed-by: Peter Zijlstra --- arch/x86/xen/enlighten.c | 65 ++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 65 insertions(+) (limited to 'arch/x86/xen/enlighten.c') diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c index 84e5adbd0925..1887435af2fb 100644 --- a/arch/x86/xen/enlighten.c +++ b/arch/x86/xen/enlighten.c @@ -2,6 +2,7 @@ #include #include +#include #include #include #include @@ -23,6 +24,9 @@ EXPORT_SYMBOL_GPL(hypercall_page); +DEFINE_STATIC_CALL(xen_hypercall, xen_hypercall_hvm); +EXPORT_STATIC_CALL_TRAMP(xen_hypercall); + /* * Pointer to the xen_vcpu_info structure or * &HYPERVISOR_shared_info->vcpu_info[cpu]. See xen_hvm_init_shared_info @@ -68,6 +72,67 @@ EXPORT_SYMBOL(xen_start_flags); */ struct shared_info *HYPERVISOR_shared_info = &xen_dummy_shared_info; +static __ref void xen_get_vendor(void) +{ + init_cpu_devs(); + cpu_detect(&boot_cpu_data); + get_cpu_vendor(&boot_cpu_data); +} + +void xen_hypercall_setfunc(void) +{ + if (static_call_query(xen_hypercall) != xen_hypercall_hvm) + return; + + if ((boot_cpu_data.x86_vendor == X86_VENDOR_AMD || + boot_cpu_data.x86_vendor == X86_VENDOR_HYGON)) + static_call_update(xen_hypercall, xen_hypercall_amd); + else + static_call_update(xen_hypercall, xen_hypercall_intel); +} + +/* + * Evaluate processor vendor in order to select the correct hypercall + * function for HVM/PVH guests. + * Might be called very early in boot before vendor has been set by + * early_cpu_init(). + */ +noinstr void *__xen_hypercall_setfunc(void) +{ + void (*func)(void); + + /* + * Xen is supported only on CPUs with CPUID, so testing for + * X86_FEATURE_CPUID is a test for early_cpu_init() having been + * run. + * + * Note that __xen_hypercall_setfunc() is noinstr only due to a nasty + * dependency chain: it is being called via the xen_hypercall static + * call when running as a PVH or HVM guest. Hypercalls need to be + * noinstr due to PV guests using hypercalls in noinstr code. So we + * can safely tag the function body as "instrumentation ok", since + * the PV guest requirement is not of interest here (xen_get_vendor() + * calls noinstr functions, and static_call_update_early() might do + * so, too). + */ + instrumentation_begin(); + + if (!boot_cpu_has(X86_FEATURE_CPUID)) + xen_get_vendor(); + + if ((boot_cpu_data.x86_vendor == X86_VENDOR_AMD || + boot_cpu_data.x86_vendor == X86_VENDOR_HYGON)) + func = xen_hypercall_amd; + else + func = xen_hypercall_intel; + + static_call_update_early(xen_hypercall, func); + + instrumentation_end(); + + return func; +} + static int xen_cpu_up_online(unsigned int cpu) { xen_init_lock_cpu(cpu); -- cgit v1.2.3 From 7fa0da5373685e7ed249af3fa317ab1e1ba8b0a6 Mon Sep 17 00:00:00 2001 From: Juergen Gross Date: Thu, 17 Oct 2024 15:27:31 +0200 Subject: x86/xen: remove hypercall page The hypercall page is no longer needed. It can be removed, as from the Xen perspective it is optional. But, from Linux's perspective, it removes naked RET instructions that escape the speculative protections that Call Depth Tracking and/or Untrain Ret are trying to achieve. This is part of XSA-466 / CVE-2024-53241. Reported-by: Andrew Cooper Signed-off-by: Juergen Gross Reviewed-by: Andrew Cooper Reviewed-by: Jan Beulich --- arch/x86/xen/enlighten.c | 2 -- 1 file changed, 2 deletions(-) (limited to 'arch/x86/xen/enlighten.c') diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c index 1887435af2fb..43dcd8c7badc 100644 --- a/arch/x86/xen/enlighten.c +++ b/arch/x86/xen/enlighten.c @@ -22,8 +22,6 @@ #include "xen-ops.h" -EXPORT_SYMBOL_GPL(hypercall_page); - DEFINE_STATIC_CALL(xen_hypercall, xen_hypercall_hvm); EXPORT_STATIC_CALL_TRAMP(xen_hypercall); -- cgit v1.2.3