x86/xen: add central hypercall functions

commit b4845bb6383821a9516ce30af3a27dc873e37fd4 upstream.

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 <andrew.cooper3@citrix.com>
Signed-off-by: Juergen Gross <jgross@suse.com>
Co-developed-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

7 files changed, 188 insertions, 1 deletions

diff --git a/arch/x86/include/asm/xen/hypercall.h b/arch/x86/include/asm/xen/hypercall.h
index 454b20815f35..82ef730aab25 100644
--- a/arch/x86/include/asm/xen/hypercall.h
+++ b/arch/x86/include/asm/xen/hypercall.h
@@ -88,6 +88,9 @@ struct xen_dm_op_buf;
 
 extern struct { char _entry[32]; } hypercall_page[];
 
+void xen_hypercall_func(void);
+DECLARE_STATIC_CALL(xen_hypercall, xen_hypercall_func);
+
 #define __HYPERCALL		"call hypercall_page+%c[offset]"
 #define __HYPERCALL_ENTRY(x)						\
 	[offset] "i" (__HYPERVISOR_##x * sizeof(hypercall_page[0]))
diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index 0f68c6da7382..de78a0762fda 100644
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -4,6 +4,7 @@
 #include <linux/memblock.h>
 #endif
 #include <linux/cpu.h>
+#include <linux/instrumentation.h>
 #include <linux/kexec.h>
 #include <linux/slab.h>
 
@@ -22,6 +23,9 @@
 
 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
@@ -94,6 +98,67 @@ struct shared_info *HYPERVISOR_shared_info = &xen_dummy_shared_info;
  */
 int xen_have_vcpu_info_placement = 1;
 
+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_KEY(xen_hypercall).func != 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);
diff --git a/arch/x86/xen/enlighten_hvm.c b/arch/x86/xen/enlighten_hvm.c
index ec50b7423a4c..f591fc5f7022 100644
--- a/arch/x86/xen/enlighten_hvm.c
+++ b/arch/x86/xen/enlighten_hvm.c
@@ -284,6 +284,10 @@ static uint32_t __init xen_platform_hvm(void)
 	if (xen_pv_domain())
 		return 0;
 
+	/* Set correct hypercall function. */
+	if (xen_domain)
+		xen_hypercall_setfunc();
+
 	if (xen_pvh_domain() && nopv) {
 		/* Guest booting via the Xen-PVH boot entry goes here */
 		pr_info("\"nopv\" parameter is ignored in PVH guest\n");
diff --git a/arch/x86/xen/enlighten_pv.c b/arch/x86/xen/enlighten_pv.c
index b1efc4b4f42a..c2cd3074e19d 100644
--- a/arch/x86/xen/enlighten_pv.c
+++ b/arch/x86/xen/enlighten_pv.c
@@ -1220,6 +1220,9 @@ asmlinkage __visible void __init xen_start_kernel(void)
 
 	xen_domain_type = XEN_PV_DOMAIN;
 	xen_start_flags = xen_start_info->flags;
+	/* Interrupts are guaranteed to be off initially. */
+	early_boot_irqs_disabled = true;
+	static_call_update_early(xen_hypercall, xen_hypercall_pv);
 
 	xen_setup_features();
 
@@ -1324,7 +1327,6 @@ asmlinkage __visible void __init xen_start_kernel(void)
 	WARN_ON(xen_cpuhp_setup(xen_cpu_up_prepare_pv, xen_cpu_dead_pv));
 
 	local_irq_disable();
-	early_boot_irqs_disabled = true;
 
 	xen_raw_console_write("mapping kernel into physical memory\n");
 	xen_setup_kernel_pagetable((pgd_t *)xen_start_info->pt_base,
diff --git a/arch/x86/xen/xen-asm.S b/arch/x86/xen/xen-asm.S
index 94bed27f6729..2055206b0f41 100644
--- a/arch/x86/xen/xen-asm.S
+++ b/arch/x86/xen/xen-asm.S
@@ -20,9 +20,31 @@
 
 #include <linux/init.h>
 #include <linux/linkage.h>
+#include <linux/objtool.h>
 #include <../entry/calling.h>
 
 /*
+ * PV hypercall interface to the hypervisor.
+ *
+ * Called via inline asm(), so better preserve %rcx and %r11.
+ *
+ * Input:
+ *	%eax: hypercall number
+ *	%rdi, %rsi, %rdx, %r10, %r8: args 1..5 for the hypercall
+ * Output: %rax
+ */
+SYM_FUNC_START(xen_hypercall_pv)
+	push %rcx
+	push %r11
+	UNWIND_HINT_SAVE
+	syscall
+	UNWIND_HINT_RESTORE
+	pop %r11
+	pop %rcx
+	RET
+SYM_FUNC_END(xen_hypercall_pv)
+
+/*
  * Enable events.  This clears the event mask and tests the pending
  * event status with one and operation.  If there are pending events,
  * then enter the hypervisor to get them handled.
diff --git a/arch/x86/xen/xen-head.S b/arch/x86/xen/xen-head.S
index 2a3ef5fcba34..61f904daee85 100644
--- a/arch/x86/xen/xen-head.S
+++ b/arch/x86/xen/xen-head.S
@@ -6,9 +6,11 @@
 
 #include <linux/elfnote.h>
 #include <linux/init.h>
+#include <linux/instrumentation.h>
 
 #include <asm/boot.h>
 #include <asm/asm.h>
+#include <asm/frame.h>
 #include <asm/msr.h>
 #include <asm/page_types.h>
 #include <asm/percpu.h>
@@ -64,6 +66,86 @@ SYM_CODE_END(asm_cpu_bringup_and_idle)
 #endif
 #endif
 
+	.pushsection .text
+/*
+ * Xen hypercall interface to the hypervisor.
+ *
+ * Input:
+ *     %eax: hypercall number
+ *   32-bit:
+ *     %ebx, %ecx, %edx, %esi, %edi: args 1..5 for the hypercall
+ *   64-bit:
+ *     %rdi, %rsi, %rdx, %r10, %r8: args 1..5 for the hypercall
+ * Output: %[er]ax
+ */
+SYM_FUNC_START(xen_hypercall_hvm)
+	FRAME_BEGIN
+	/* Save all relevant registers (caller save and arguments). */
+#ifdef CONFIG_X86_32
+	push %eax
+	push %ebx
+	push %ecx
+	push %edx
+	push %esi
+	push %edi
+#else
+	push %rax
+	push %rcx
+	push %rdx
+	push %rdi
+	push %rsi
+	push %r11
+	push %r10
+	push %r9
+	push %r8
+#ifdef CONFIG_FRAME_POINTER
+	pushq $0	/* Dummy push for stack alignment. */
+#endif
+#endif
+	/* Set the vendor specific function. */
+	call __xen_hypercall_setfunc
+	/* Set ZF = 1 if AMD, Restore saved registers. */
+#ifdef CONFIG_X86_32
+	lea xen_hypercall_amd, %ebx
+	cmp %eax, %ebx
+	pop %edi
+	pop %esi
+	pop %edx
+	pop %ecx
+	pop %ebx
+	pop %eax
+#else
+	lea xen_hypercall_amd(%rip), %rbx
+	cmp %rax, %rbx
+#ifdef CONFIG_FRAME_POINTER
+	pop %rax	/* Dummy pop. */
+#endif
+	pop %r8
+	pop %r9
+	pop %r10
+	pop %r11
+	pop %rsi
+	pop %rdi
+	pop %rdx
+	pop %rcx
+	pop %rax
+#endif
+	/* Use correct hypercall function. */
+	jz xen_hypercall_amd
+	jmp xen_hypercall_intel
+SYM_FUNC_END(xen_hypercall_hvm)
+
+SYM_FUNC_START(xen_hypercall_amd)
+	vmmcall
+	RET
+SYM_FUNC_END(xen_hypercall_amd)
+
+SYM_FUNC_START(xen_hypercall_intel)
+	vmcall
+	RET
+SYM_FUNC_END(xen_hypercall_intel)
+	.popsection
+
 .pushsection .text
 	.balign PAGE_SIZE
 SYM_CODE_START(hypercall_page)
diff --git a/arch/x86/xen/xen-ops.h b/arch/x86/xen/xen-ops.h
index 98242430d07e..2fc9077290db 100644
--- a/arch/x86/xen/xen-ops.h
+++ b/arch/x86/xen/xen-ops.h
@@ -161,4 +161,13 @@ void xen_hvm_post_suspend(int suspend_cancelled);
 static inline void xen_hvm_post_suspend(int suspend_cancelled) {}
 #endif
 
+#ifdef CONFIG_XEN_PV
+void xen_hypercall_pv(void);
+#endif
+void xen_hypercall_hvm(void);
+void xen_hypercall_amd(void);
+void xen_hypercall_intel(void);
+void xen_hypercall_setfunc(void);
+void *__xen_hypercall_setfunc(void);
+
 #endif /* XEN_OPS_H */