[PATCH v3 26/39] x86/ibt: Annotate text references

Peter Zijlstra
2022-03-03T11:33:34Z

Annotate away some of the generic code references. This is things
where we take the address of a symbol for exception handling or return
addresses (eg. context switch).

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
arch/x86/entry/entry_64.S | 6 ++++++
arch/x86/entry/entry_64_compat.S | 1 +
arch/x86/kernel/alternative.c | 9 +++++++--
arch/x86/kernel/head_64.S | 4 ++++
arch/x86/kernel/kprobes/core.c | 1 +
arch/x86/kernel/relocate_kernel_64.S | 2 ++
arch/x86/lib/error-inject.c | 2 ++
arch/x86/lib/retpoline.S | 1 +
8 files changed, 24 insertions(+), 2 deletions(-)

--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -277,6 +277,7 @@ SYM_FUNC_END(__switch_to_asm)
.pushsection .text, "ax"
SYM_CODE_START(ret_from_fork)
UNWIND_HINT_EMPTY
+ ANNOTATE_NOENDBR // copy_thread
movq %rax, %rdi
call schedule_tail /* rdi: 'prev' task parameter */

@@ -569,6 +570,7 @@ SYM_CODE_END(\asmsym)
.align 16
.globl __irqentry_text_end
__irqentry_text_end:
+ ANNOTATE_NOENDBR

SYM_CODE_START_LOCAL(common_interrupt_return)
SYM_INNER_LABEL(swapgs_restore_regs_and_return_to_usermode, SYM_L_GLOBAL)
@@ -650,6 +652,7 @@ SYM_INNER_LABEL(early_xen_iret_patch, SY
#endif

SYM_INNER_LABEL(native_irq_return_iret, SYM_L_GLOBAL)
+ ANNOTATE_NOENDBR // exc_double_fault
/*
* This may fault. Non-paranoid faults on return to userspace are
* handled by fixup_bad_iret. These include #SS, #GP, and #NP.
@@ -744,6 +747,7 @@ SYM_FUNC_START(asm_load_gs_index)
FRAME_BEGIN
swapgs
.Lgs_change:
+ ANNOTATE_NOENDBR // error_entry
movl %edi, %gs
2: ALTERNATIVE "", "mfence", X86_BUG_SWAPGS_FENCE
swapgs
@@ -1322,6 +1326,7 @@ SYM_CODE_START(asm_exc_nmi)
#endif

repeat_nmi:
+ ANNOTATE_NOENDBR // this code
/*
* If there was a nested NMI, the first NMI's iret will return
* here. But NMIs are still enabled and we can take another
@@ -1350,6 +1355,7 @@ SYM_CODE_START(asm_exc_nmi)
.endr
subq $(5*8), %rsp
end_repeat_nmi:
+ ANNOTATE_NOENDBR // this code

/*
* Everything below this point can be preempted by a nested NMI.
--- a/arch/x86/entry/entry_64_compat.S
+++ b/arch/x86/entry/entry_64_compat.S
@@ -148,6 +148,7 @@ SYM_INNER_LABEL(entry_SYSENTER_compat_af
popfq
jmp .Lsysenter_flags_fixed
SYM_INNER_LABEL(__end_entry_SYSENTER_compat, SYM_L_GLOBAL)
+ ANNOTATE_NOENDBR // is_sysenter_singlestep
SYM_CODE_END(entry_SYSENTER_compat)

/*
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -713,6 +713,7 @@ asm (
" .pushsection .init.text, \"ax\", @progbits\n"
" .type int3_magic, @function\n"
"int3_magic:\n"
+ ANNOTATE_NOENDBR
" movl $1, (%" _ASM_ARG1 ")\n"
ASM_RET
" .size int3_magic, .-int3_magic\n"
@@ -724,16 +725,19 @@ extern void int3_selftest_ip(void); /* d
static int __init
int3_exception_notify(struct notifier_block *self, unsigned long val, void *data)
{
+ unsigned long selftest = (unsigned long)&int3_selftest_ip;
struct die_args *args = data;
struct pt_regs *regs = args->regs;

+ OPTIMIZER_HIDE_VAR(selftest);
+
if (!regs || user_mode(regs))
return NOTIFY_DONE;

if (val != DIE_INT3)
return NOTIFY_DONE;

- if (regs->ip - INT3_INSN_SIZE != (unsigned long)&int3_selftest_ip)
+ if (regs->ip - INT3_INSN_SIZE != selftest)
return NOTIFY_DONE;

int3_emulate_call(regs, (unsigned long)&int3_magic);
@@ -757,7 +761,8 @@ static void __init int3_selftest(void)
* then trigger the INT3, padded with NOPs to match a CALL instruction
* length.
*/
- asm volatile ("int3_selftest_ip: int3; nop; nop; nop; nop\n\t"
+ asm volatile (ANNOTATE_NOENDBR
+ "int3_selftest_ip: int3; nop; nop; nop; nop\n\t"
: ASM_CALL_CONSTRAINT
: __ASM_SEL_RAW(a, D) (&val)
: "memory");
--- a/arch/x86/kernel/head_64.S
+++ b/arch/x86/kernel/head_64.S
@@ -99,6 +99,7 @@ SYM_CODE_END(startup_64)

SYM_CODE_START(secondary_startup_64)
UNWIND_HINT_EMPTY
+ ANNOTATE_NOENDBR
/*
* At this point the CPU runs in 64bit mode CS.L = 1 CS.D = 0,
* and someone has loaded a mapped page table.
@@ -127,6 +128,7 @@ SYM_CODE_START(secondary_startup_64)
*/
SYM_INNER_LABEL(secondary_startup_64_no_verify, SYM_L_GLOBAL)
UNWIND_HINT_EMPTY
+ ANNOTATE_NOENDBR

/*
* Retrieve the modifier (SME encryption mask if SME is active) to be
@@ -192,6 +194,7 @@ SYM_INNER_LABEL(secondary_startup_64_no_
jmp *%rax
1:
UNWIND_HINT_EMPTY
+ ANNOTATE_NOENDBR // above

/*
* We must switch to a new descriptor in kernel space for the GDT
@@ -299,6 +302,7 @@ SYM_INNER_LABEL(secondary_startup_64_no_
pushq %rax # target address in negative space
lretq
.Lafter_lret:
+ ANNOTATE_NOENDBR
SYM_CODE_END(secondary_startup_64)

#include "verify_cpu.S"
--- a/arch/x86/kernel/kprobes/core.c
+++ b/arch/x86/kernel/kprobes/core.c
@@ -1040,6 +1040,7 @@ asm(
".type __kretprobe_trampoline, @function\n"
"__kretprobe_trampoline:\n"
#ifdef CONFIG_X86_64
+ ANNOTATE_NOENDBR
/* Push a fake return address to tell the unwinder it's a kretprobe. */
" pushq $__kretprobe_trampoline\n"
UNWIND_HINT_FUNC
--- a/arch/x86/kernel/relocate_kernel_64.S
+++ b/arch/x86/kernel/relocate_kernel_64.S
@@ -42,6 +42,7 @@
.code64
SYM_CODE_START_NOALIGN(relocate_kernel)
UNWIND_HINT_EMPTY
+ ANNOTATE_NOENDBR
/*
* %rdi indirection_page
* %rsi page_list
@@ -223,6 +224,7 @@ SYM_CODE_END(identity_mapped)

SYM_CODE_START_LOCAL_NOALIGN(virtual_mapped)
UNWIND_HINT_EMPTY
+ ANNOTATE_NOENDBR // RET target, above
movq RSP(%r8), %rsp
movq CR4(%r8), %rax
movq %rax, %cr4
--- a/arch/x86/lib/error-inject.c
+++ b/arch/x86/lib/error-inject.c
@@ -3,6 +3,7 @@
#include <linux/linkage.h>
#include <linux/error-injection.h>
#include <linux/kprobes.h>
+#include <linux/objtool.h>

asmlinkage void just_return_func(void);

@@ -11,6 +12,7 @@ asm(
".type just_return_func, @function\n"
".globl just_return_func\n"
"just_return_func:\n"
+ ANNOTATE_NOENDBR
ASM_RET
".size just_return_func, .-just_return_func\n"
);
--- a/arch/x86/lib/retpoline.S
+++ b/arch/x86/lib/retpoline.S
@@ -55,6 +55,7 @@ SYM_INNER_LABEL(__x86_indirect_thunk_\re

.align RETPOLINE_THUNK_SIZE
SYM_CODE_START(__x86_indirect_thunk_array)
+ ANNOTATE_NOENDBR // apply_retpolines

#define GEN(reg) THUNK reg
#include <asm/GEN-for-each-reg.h>