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x86/xen: remove hypercall page

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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 <andrew.cooper3@citrix.com>
Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
This commit is contained in:
Juergen Gross 2024-10-17 15:27:31 +02:00
parent b1c2cb86f4
commit 7fa0da5373
7 changed files with 1 additions and 52 deletions
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2
arch/x86/include/asm/xen/hypercall.h
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@ -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);

5
arch/x86/kernel/callthunks.c
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@ -142,11 +142,6 @@ 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;
}

4
arch/x86/kernel/vmlinux.lds.S
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@ -519,14 +519,10 @@ INIT_PER_CPU(irq_stack_backing_store);
* linker will never mark as relocatable. (Using just ABSOLUTE() is not
* sufficient for that).
*/
#ifdef CONFIG_XEN
#ifdef CONFIG_XEN_PV
xen_elfnote_entry_value =
ABSOLUTE(xen_elfnote_entry) + ABSOLUTE(startup_xen);
#endif
xen_elfnote_hypercall_page_value =
ABSOLUTE(xen_elfnote_hypercall_page) + ABSOLUTE(hypercall_page);
#endif
#ifdef CONFIG_PVH
xen_elfnote_phys32_entry_value =
ABSOLUTE(xen_elfnote_phys32_entry) + ABSOLUTE(pvh_start_xen - LOAD_OFFSET);

2
arch/x86/xen/enlighten.c
View File

@ -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);

9
arch/x86/xen/enlighten_hvm.c
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@ -106,15 +106,8 @@ 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();

7
arch/x86/xen/enlighten_pvh.c
View File

@ -129,17 +129,10 @@ static void __init pvh_arch_setup(void)
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));
x86_init.oem.arch_setup = pvh_arch_setup;
x86_init.oem.banner = xen_banner;

24
arch/x86/xen/xen-head.S
View File

@ -22,28 +22,6 @@
#include <xen/interface/xen-mca.h>
#include <asm/xen/interface.h>
.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 <asm/xen-hypercalls.h>
#undef HYPERCALL
SYM_CODE_END(hypercall_page)
.popsection
#ifdef CONFIG_XEN_PV
__INIT
SYM_CODE_START(startup_xen)
@ -199,8 +177,6 @@ SYM_FUNC_END(xen_hypercall_intel)
#else
# define FEATURES_DOM0 0
#endif
ELFNOTE(Xen, XEN_ELFNOTE_HYPERCALL_PAGE, .globl xen_elfnote_hypercall_page;
xen_elfnote_hypercall_page: _ASM_PTR xen_elfnote_hypercall_page_value - .)
ELFNOTE(Xen, XEN_ELFNOTE_SUPPORTED_FEATURES,
.long FEATURES_PV | FEATURES_PVH | FEATURES_DOM0)
ELFNOTE(Xen, XEN_ELFNOTE_LOADER, .asciz "generic")