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Subject[PATCH v2 8/8] x86/head: Add unwind hint annotations
Date
Jiri Slaby reported an ORC issue when unwinding from an idle task.  The
stack was:

ffffffff811083c2 do_idle+0x142/0x1e0
ffffffff8110861d cpu_startup_entry+0x5d/0x60
ffffffff82715f58 start_kernel+0x3ff/0x407
ffffffff827153e8 x86_64_start_kernel+0x14e/0x15d
ffffffff810001bf secondary_startup_64+0x9f/0xa0

The ORC unwinder errored out at secondary_startup_64 because the head
code isn't annotated yet so there wasn't a corresponding ORC entry.

Fix that and any other head-related unwinding issues by adding unwind
hints to the head code.

Reported-by: Jiri Slaby <jslaby@suse.cz>
Tested-by: Jiri Slaby <jslaby@suse.cz>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
---
arch/x86/kernel/Makefile | 1 -
arch/x86/kernel/head_64.S | 14 ++++++++++++--
2 files changed, 12 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
index fd0a7895b63f..d8e2b700d1db 100644
--- a/arch/x86/kernel/Makefile
+++ b/arch/x86/kernel/Makefile
@@ -26,7 +26,6 @@ KASAN_SANITIZE_dumpstack.o := n
KASAN_SANITIZE_dumpstack_$(BITS).o := n
KASAN_SANITIZE_stacktrace.o := n

-OBJECT_FILES_NON_STANDARD_head_$(BITS).o := y
OBJECT_FILES_NON_STANDARD_relocate_kernel_$(BITS).o := y
OBJECT_FILES_NON_STANDARD_ftrace_$(BITS).o := y
OBJECT_FILES_NON_STANDARD_test_nx.o := y
diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
index edacd579d504..42e32c2e51bb 100644
--- a/arch/x86/kernel/head_64.S
+++ b/arch/x86/kernel/head_64.S
@@ -49,6 +49,7 @@ L3_START_KERNEL = pud_index(__START_KERNEL_map)
.code64
.globl startup_64
startup_64:
+ UNWIND_HINT_EMPTY
/*
* At this point the CPU runs in 64bit mode CS.L = 1 CS.D = 0,
* and someone has loaded an identity mapped page table
@@ -88,6 +89,7 @@ startup_64:
addq $(early_top_pgt - __START_KERNEL_map), %rax
jmp 1f
ENTRY(secondary_startup_64)
+ UNWIND_HINT_EMPTY
/*
* At this point the CPU runs in 64bit mode CS.L = 1 CS.D = 0,
* and someone has loaded a mapped page table.
@@ -132,6 +134,7 @@ ENTRY(secondary_startup_64)
movq $1f, %rax
jmp *%rax
1:
+ UNWIND_HINT_EMPTY

/* Check if nx is implemented */
movl $0x80000001, %eax
@@ -246,6 +249,7 @@ END(secondary_startup_64)
*/
ENTRY(start_cpu0)
movq initial_stack(%rip), %rsp
+ UNWIND_HINT_EMPTY
jmp .Ljump_to_C_code
ENDPROC(start_cpu0)
#endif
@@ -270,13 +274,18 @@ ENTRY(early_idt_handler_array)
i = 0
.rept NUM_EXCEPTION_VECTORS
.ifeq (EXCEPTION_ERRCODE_MASK >> i) & 1
- pushq $0 # Dummy error code, to make stack frame uniform
+ UNWIND_HINT_IRET_REGS
+ pushq $0 # Dummy error code, to make stack frame uniform
+ .else
+ UNWIND_HINT_IRET_REGS offset=8
.endif
pushq $i # 72(%rsp) Vector number
jmp early_idt_handler_common
+ UNWIND_HINT_IRET_REGS
i = i + 1
.fill early_idt_handler_array + i*EARLY_IDT_HANDLER_SIZE - ., 1, 0xcc
.endr
+ UNWIND_HINT_IRET_REGS offset=16
END(early_idt_handler_array)

early_idt_handler_common:
@@ -305,6 +314,7 @@ early_idt_handler_common:
pushq %r13 /* pt_regs->r13 */
pushq %r14 /* pt_regs->r14 */
pushq %r15 /* pt_regs->r15 */
+ UNWIND_HINT_REGS

cmpq $14,%rsi /* Page fault? */
jnz 10f
@@ -427,7 +437,7 @@ ENTRY(phys_base)
EXPORT_SYMBOL(phys_base)

#include "../../x86/xen/xen-head.S"
-
+
__PAGE_ALIGNED_BSS
NEXT_PAGE(empty_zero_page)
.skip PAGE_SIZE
--
2.13.5
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