From bcf0e2fda80c69392489d7739708409b7db1c865 Mon Sep 17 00:00:00 2001 From: Juergen Gross Date: Thu, 17 Oct 2024 15:27:31 +0200 Subject: [PATCH] x86/xen: remove hypercall page commit 7fa0da5373685e7ed249af3fa317ab1e1ba8b0a6 upstream. 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 Signed-off-by: Greg Kroah-Hartman --- arch/x86/include/asm/xen/hypercall.h | 2 -- arch/x86/kernel/callthunks.c | 5 ----- arch/x86/xen/enlighten.c | 2 -- arch/x86/xen/enlighten_hvm.c | 9 +-------- arch/x86/xen/enlighten_pvh.c | 7 ------- arch/x86/xen/xen-head.S | 23 ----------------------- 6 files changed, 1 insertion(+), 47 deletions(-) diff --git a/arch/x86/include/asm/xen/hypercall.h b/arch/x86/include/asm/xen/hypercall.h index 7d5f8ad66774..97771b9d33af 100644 --- a/arch/x86/include/asm/xen/hypercall.h +++ b/arch/x86/include/asm/xen/hypercall.h @@ -88,8 +88,6 @@ struct xen_dm_op_buf; * there aren't more than 5 arguments...) */ -extern struct { char _entry[32]; } hypercall_page[]; - void xen_hypercall_func(void); DECLARE_STATIC_CALL(xen_hypercall, xen_hypercall_func); diff --git a/arch/x86/kernel/callthunks.c b/arch/x86/kernel/callthunks.c index faa9f2299848..e78d5366b9e3 100644 --- a/arch/x86/kernel/callthunks.c +++ b/arch/x86/kernel/callthunks.c @@ -145,11 +145,6 @@ static bool skip_addr(void *dest) if (dest >= (void *)relocate_kernel && dest < (void*)relocate_kernel + KEXEC_CONTROL_CODE_MAX_SIZE) return true; -#endif -#ifdef CONFIG_XEN - if (dest >= (void *)hypercall_page && - dest < (void*)hypercall_page + PAGE_SIZE) - return true; #endif return false; } diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c index 883ce85bb064..0219f1c90202 100644 --- a/arch/x86/xen/enlighten.c +++ b/arch/x86/xen/enlighten.c @@ -27,8 +27,6 @@ #include "smp.h" #include "pmu.h" -EXPORT_SYMBOL_GPL(hypercall_page); - DEFINE_STATIC_CALL(xen_hypercall, xen_hypercall_hvm); EXPORT_STATIC_CALL_TRAMP(xen_hypercall); diff --git a/arch/x86/xen/enlighten_hvm.c b/arch/x86/xen/enlighten_hvm.c index c8478e0314a2..70be57e8f51c 100644 --- a/arch/x86/xen/enlighten_hvm.c +++ b/arch/x86/xen/enlighten_hvm.c @@ -108,15 +108,8 @@ static void __init init_hvm_pv_info(void) /* PVH set up hypercall page in xen_prepare_pvh(). */ if (xen_pvh_domain()) pv_info.name = "Xen PVH"; - else { - u64 pfn; - uint32_t msr; - + else pv_info.name = "Xen HVM"; - msr = cpuid_ebx(base + 2); - pfn = __pa(hypercall_page); - wrmsr_safe(msr, (u32)pfn, (u32)(pfn >> 32)); - } xen_setup_features(); diff --git a/arch/x86/xen/enlighten_pvh.c b/arch/x86/xen/enlighten_pvh.c index c28f073c1df5..60b358c2f434 100644 --- a/arch/x86/xen/enlighten_pvh.c +++ b/arch/x86/xen/enlighten_pvh.c @@ -28,17 +28,10 @@ EXPORT_SYMBOL_GPL(xen_pvh); void __init xen_pvh_init(struct boot_params *boot_params) { - u32 msr; - u64 pfn; - xen_pvh = 1; xen_domain_type = XEN_HVM_DOMAIN; xen_start_flags = pvh_start_info.flags; - msr = cpuid_ebx(xen_cpuid_base() + 2); - pfn = __pa(hypercall_page); - wrmsr_safe(msr, (u32)pfn, (u32)(pfn >> 32)); - if (xen_initial_domain()) x86_init.oem.arch_setup = xen_add_preferred_consoles; x86_init.oem.banner = xen_banner; diff --git a/arch/x86/xen/xen-head.S b/arch/x86/xen/xen-head.S index 14fed5eb025f..4fd814321ed0 100644 --- a/arch/x86/xen/xen-head.S +++ b/arch/x86/xen/xen-head.S @@ -22,28 +22,6 @@ #include #include -.pushsection .noinstr.text, "ax" - .balign PAGE_SIZE -SYM_CODE_START(hypercall_page) - .rept (PAGE_SIZE / 32) - UNWIND_HINT_FUNC - ANNOTATE_NOENDBR - ANNOTATE_UNRET_SAFE - ret - /* - * Xen will write the hypercall page, and sort out ENDBR. - */ - .skip 31, 0xcc - .endr - -#define HYPERCALL(n) \ - .equ xen_hypercall_##n, hypercall_page + __HYPERVISOR_##n * 32; \ - .type xen_hypercall_##n, @function; .size xen_hypercall_##n, 32 -#include -#undef HYPERCALL -SYM_CODE_END(hypercall_page) -.popsection - #ifdef CONFIG_XEN_PV __INIT SYM_CODE_START(startup_xen) @@ -198,7 +176,6 @@ SYM_FUNC_END(xen_hypercall_intel) #else # define FEATURES_DOM0 0 #endif - ELFNOTE(Xen, XEN_ELFNOTE_HYPERCALL_PAGE, _ASM_PTR hypercall_page) ELFNOTE(Xen, XEN_ELFNOTE_SUPPORTED_FEATURES, .long FEATURES_PV | FEATURES_PVH | FEATURES_DOM0) ELFNOTE(Xen, XEN_ELFNOTE_LOADER, .asciz "generic")