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Subject[tip: x86/core] x86/ibt,xen: Sprinkle the ENDBR
The following commit has been merged into the x86/core branch of tip:

Commit-ID: 745fc9ec4d0d007b72ae688525560ba39cdef784
Gitweb: https://git.kernel.org/tip/745fc9ec4d0d007b72ae688525560ba39cdef784
Author: Peter Zijlstra <peterz@infradead.org>
AuthorDate: Tue, 08 Mar 2022 16:30:23 +01:00
Committer: Peter Zijlstra <peterz@infradead.org>
CommitterDate: Tue, 08 Mar 2022 23:53:29 +01:00

x86/ibt,xen: Sprinkle the ENDBR

Even though Xen currently doesn't advertise IBT, prepare for when it
will eventually do so and sprinkle the ENDBR dust accordingly.

Even though most of the entry points are IRET like, the CPL0
Hypervisor can set WAIT-FOR-ENDBR and demand ENDBR at these sites.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Link: https://lore.kernel.org/r/20220308154317.873919996@infradead.org
---
arch/x86/entry/entry_64.S | 1 +
arch/x86/include/asm/segment.h | 2 +-
arch/x86/kernel/head_64.S | 1 +
arch/x86/xen/enlighten_pv.c | 3 +++
arch/x86/xen/xen-asm.S | 9 +++++++++
arch/x86/xen/xen-head.S | 9 +++++++--
6 files changed, 22 insertions(+), 3 deletions(-)

diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index f731393..3fd3828 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -809,6 +809,7 @@ SYM_CODE_END(exc_xen_hypervisor_callback)
*/
SYM_CODE_START(xen_failsafe_callback)
UNWIND_HINT_EMPTY
+ ENDBR
movl %ds, %ecx
cmpw %cx, 0x10(%rsp)
jne 1f
diff --git a/arch/x86/include/asm/segment.h b/arch/x86/include/asm/segment.h
index b228c9d..3a31d4e 100644
--- a/arch/x86/include/asm/segment.h
+++ b/arch/x86/include/asm/segment.h
@@ -283,7 +283,7 @@ static inline void vdso_read_cpunode(unsigned *cpu, unsigned *node)
* pop %rcx; pop %r11; jmp early_idt_handler_array[i]; summing up to
* max 8 bytes.
*/
-#define XEN_EARLY_IDT_HANDLER_SIZE 8
+#define XEN_EARLY_IDT_HANDLER_SIZE (8 + ENDBR_INSN_SIZE)

#ifndef __ASSEMBLY__

diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
index 023761c..990960a 100644
--- a/arch/x86/kernel/head_64.S
+++ b/arch/x86/kernel/head_64.S
@@ -383,6 +383,7 @@ SYM_CODE_START(early_idt_handler_array)
.endr
UNWIND_HINT_IRET_REGS offset=16
SYM_CODE_END(early_idt_handler_array)
+ ANNOTATE_NOENDBR // early_idt_handler_array[NUM_EXCEPTION_VECTORS]

SYM_CODE_START_LOCAL(early_idt_handler_common)
/*
diff --git a/arch/x86/xen/enlighten_pv.c b/arch/x86/xen/enlighten_pv.c
index 3c7a55c..5038edb 100644
--- a/arch/x86/xen/enlighten_pv.c
+++ b/arch/x86/xen/enlighten_pv.c
@@ -624,6 +624,9 @@ static struct trap_array_entry trap_array[] = {
TRAP_ENTRY(exc_coprocessor_error, false ),
TRAP_ENTRY(exc_alignment_check, false ),
TRAP_ENTRY(exc_simd_coprocessor_error, false ),
+#ifdef CONFIG_X86_KERNEL_IBT
+ TRAP_ENTRY(exc_control_protection, false ),
+#endif
};

static bool __ref get_trap_addr(void **addr, unsigned int ist)
diff --git a/arch/x86/xen/xen-asm.S b/arch/x86/xen/xen-asm.S
index ee17b94..caa9bc2 100644
--- a/arch/x86/xen/xen-asm.S
+++ b/arch/x86/xen/xen-asm.S
@@ -122,6 +122,7 @@ SYM_FUNC_END(xen_read_cr2_direct);
.macro xen_pv_trap name
SYM_CODE_START(xen_\name)
UNWIND_HINT_EMPTY
+ ENDBR
pop %rcx
pop %r11
jmp \name
@@ -147,6 +148,9 @@ xen_pv_trap asm_exc_page_fault
xen_pv_trap asm_exc_spurious_interrupt_bug
xen_pv_trap asm_exc_coprocessor_error
xen_pv_trap asm_exc_alignment_check
+#ifdef CONFIG_X86_KERNEL_IBT
+xen_pv_trap asm_exc_control_protection
+#endif
#ifdef CONFIG_X86_MCE
xen_pv_trap asm_xenpv_exc_machine_check
#endif /* CONFIG_X86_MCE */
@@ -162,6 +166,7 @@ SYM_CODE_START(xen_early_idt_handler_array)
i = 0
.rept NUM_EXCEPTION_VECTORS
UNWIND_HINT_EMPTY
+ ENDBR
pop %rcx
pop %r11
jmp early_idt_handler_array + i*EARLY_IDT_HANDLER_SIZE
@@ -231,6 +236,7 @@ SYM_CODE_END(xenpv_restore_regs_and_return_to_usermode)
/* Normal 64-bit system call target */
SYM_CODE_START(xen_syscall_target)
UNWIND_HINT_EMPTY
+ ENDBR
popq %rcx
popq %r11

@@ -250,6 +256,7 @@ SYM_CODE_END(xen_syscall_target)
/* 32-bit compat syscall target */
SYM_CODE_START(xen_syscall32_target)
UNWIND_HINT_EMPTY
+ ENDBR
popq %rcx
popq %r11

@@ -267,6 +274,7 @@ SYM_CODE_END(xen_syscall32_target)
/* 32-bit compat sysenter target */
SYM_CODE_START(xen_sysenter_target)
UNWIND_HINT_EMPTY
+ ENDBR
/*
* NB: Xen is polite and clears TF from EFLAGS for us. This means
* that we don't need to guard against single step exceptions here.
@@ -290,6 +298,7 @@ SYM_CODE_END(xen_sysenter_target)
SYM_CODE_START(xen_syscall32_target)
SYM_CODE_START(xen_sysenter_target)
UNWIND_HINT_EMPTY
+ ENDBR
lea 16(%rsp), %rsp /* strip %rcx, %r11 */
mov $-ENOSYS, %rax
pushq $0
diff --git a/arch/x86/xen/xen-head.S b/arch/x86/xen/xen-head.S
index 11d2865..ac17196 100644
--- a/arch/x86/xen/xen-head.S
+++ b/arch/x86/xen/xen-head.S
@@ -25,8 +25,12 @@
SYM_CODE_START(hypercall_page)
.rept (PAGE_SIZE / 32)
UNWIND_HINT_FUNC
- .skip 31, 0x90
- RET
+ ANNOTATE_NOENDBR
+ ret
+ /*
+ * Xen will write the hypercall page, and sort out ENDBR.
+ */
+ .skip 31, 0xcc
.endr

#define HYPERCALL(n) \
@@ -74,6 +78,7 @@ SYM_CODE_END(startup_xen)
.pushsection .text
SYM_CODE_START(asm_cpu_bringup_and_idle)
UNWIND_HINT_EMPTY
+ ENDBR

call cpu_bringup_and_idle
SYM_CODE_END(asm_cpu_bringup_and_idle)
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