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x86/alternatives: Add int3_emulate_call() selftest

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Given that the entry_*.S changes for this functionality are somewhat
tricky, make sure the paths are tested every boot, instead of on the
rare occasion when we trip an INT3 while rewriting text.

Requested-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Josh Poimboeuf <jpoimboe@redhat.com>
Acked-by: Andy Lutomirski <luto@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Peter Zijlstra 2019-05-03 12:22:47 +02:00 committed by Ingo Molnar
parent faeedb0679
commit 7457c0da02
1 changed files with 77 additions and 4 deletions
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81
arch/x86/kernel/alternative.c
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@ -615,11 +615,83 @@ extern struct paravirt_patch_site __start_parainstructions[],
__stop_parainstructions[]; __stop_parainstructions[];
#endif /* CONFIG_PARAVIRT */ #endif /* CONFIG_PARAVIRT */
/*
* Self-test for the INT3 based CALL emulation code.
*
* This exercises int3_emulate_call() to make sure INT3 pt_regs are set up
* properly and that there is a stack gap between the INT3 frame and the
* previous context. Without this gap doing a virtual PUSH on the interrupted
* stack would corrupt the INT3 IRET frame.
*
* See entry_{32,64}.S for more details.
*/
static void __init int3_magic(unsigned int *ptr)
{
*ptr = 1;
}
extern __initdata unsigned long int3_selftest_ip; /* defined in asm below */
static int __init
int3_exception_notify(struct notifier_block *self, unsigned long val, void *data)
{
struct die_args *args = data;
struct pt_regs *regs = args->regs;
if (!regs || user_mode(regs))
return NOTIFY_DONE;
if (val != DIE_INT3)
return NOTIFY_DONE;
if (regs->ip - INT3_INSN_SIZE != int3_selftest_ip)
return NOTIFY_DONE;
int3_emulate_call(regs, (unsigned long)&int3_magic);
return NOTIFY_STOP;
}
static void __init int3_selftest(void)
{
static __initdata struct notifier_block int3_exception_nb = {
.notifier_call = int3_exception_notify,
.priority = INT_MAX-1, /* last */
};
unsigned int val = 0;
BUG_ON(register_die_notifier(&int3_exception_nb));
/*
* Basically: int3_magic(&val); but really complicated :-)
*
* Stick the address of the INT3 instruction into int3_selftest_ip,
* then trigger the INT3, padded with NOPs to match a CALL instruction
* length.
*/
asm volatile ("1: int3; nop; nop; nop; nop\n\t"
".pushsection .init.data,\"aw\"\n\t"
".align " __ASM_SEL(4, 8) "\n\t"
".type int3_selftest_ip, @object\n\t"
".size int3_selftest_ip, " __ASM_SEL(4, 8) "\n\t"
"int3_selftest_ip:\n\t"
__ASM_SEL(.long, .quad) " 1b\n\t"
".popsection\n\t"
: : __ASM_SEL_RAW(a, D) (&val) : "memory");
BUG_ON(val != 1);
unregister_die_notifier(&int3_exception_nb);
}
void __init alternative_instructions(void) void __init alternative_instructions(void)
{ {
/* The patching is not fully atomic, so try to avoid local interruptions int3_selftest();
that might execute the to be patched code.
Other CPUs are not running. */ /*
* The patching is not fully atomic, so try to avoid local
* interruptions that might execute the to be patched code.
* Other CPUs are not running.
*/
stop_nmi(); stop_nmi();
/* /*
@ -644,10 +716,11 @@ void __init alternative_instructions(void)
_text, _etext); _text, _etext);
} }
if (!uniproc_patched || num_possible_cpus() == 1) if (!uniproc_patched || num_possible_cpus() == 1) {
free_init_pages("SMP alternatives", free_init_pages("SMP alternatives",
(unsigned long)__smp_locks, (unsigned long)__smp_locks,
(unsigned long)__smp_locks_end); (unsigned long)__smp_locks_end);
}
#endif #endif
apply_paravirt(__parainstructions, __parainstructions_end); apply_paravirt(__parainstructions, __parainstructions_end);