Commit a1a5482a authored by Peter Zijlstra's avatar Peter Zijlstra
Browse files

x86/extable: Fix ex_handler_msr() print condition 



On Fri, Jun 17, 2022 at 02:08:52PM +0300, Stephane Eranian wrote:
> Some changes to the way invalid MSR accesses are reported by the
> kernel is causing some problems with messages printed on the
> console.
>
> We have seen several cases of ex_handler_msr() printing invalid MSR
> accesses once but the callstack multiple times causing confusion on
> the console.

> The problem here is that another earlier commit (5.13):
>
> a358f406 ("once: implement DO_ONCE_LITE for non-fast-path "do once" functionality")
>
> Modifies all the pr_*_once() calls to always return true claiming
> that no caller is ever checking the return value of the functions.
>
> This is why we are seeing the callstack printed without the
> associated printk() msg.

Extract the ONCE_IF(cond) part into __ONCE_LTE_IF() and use that to
implement DO_ONCE_LITE_IF() and fix the extable code.

Fixes: a358f406 ("once: implement DO_ONCE_LITE for non-fast-path "do once" functionality")
Reported-by: default avatarStephane Eranian <eranian@google.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: default avatarStephane Eranian <eranian@google.com>
Link: https://lkml.kernel.org/r/YqyVFsbviKjVGGZ9@worktop.programming.kicks-ass.net
parent 09d09531

arch/x86/mm/extable.c

+9 −7
Original line number Diff line number Diff line
@@ -94,16 +94,18 @@ static bool ex_handler_copy(const struct exception_table_entry *fixup, 
static bool ex_handler_msr(const struct exception_table_entry *fixup,

			   struct pt_regs *regs, bool wrmsr, bool safe, int reg)

{

	if (!safe && wrmsr &&

	    pr_warn_once("unchecked MSR access error: WRMSR to 0x%x (tried to write 0x%08x%08x) at rIP: 0x%lx (%pS)\n",

	if (__ONCE_LITE_IF(!safe && wrmsr)) {

		pr_warn("unchecked MSR access error: WRMSR to 0x%x (tried to write 0x%08x%08x) at rIP: 0x%lx (%pS)\n",

			(unsigned int)regs->cx, (unsigned int)regs->dx,

			 (unsigned int)regs->ax,  regs->ip, (void *)regs->ip))

			(unsigned int)regs->ax,  regs->ip, (void *)regs->ip);

		show_stack_regs(regs);

	}



	if (!safe && !wrmsr &&

	    pr_warn_once("unchecked MSR access error: RDMSR from 0x%x at rIP: 0x%lx (%pS)\n",

			 (unsigned int)regs->cx, regs->ip, (void *)regs->ip))

	if (__ONCE_LITE_IF(!safe && !wrmsr)) {

		pr_warn("unchecked MSR access error: RDMSR from 0x%x at rIP: 0x%lx (%pS)\n",

			(unsigned int)regs->cx, regs->ip, (void *)regs->ip);

		show_stack_regs(regs);

	}



	if (!wrmsr) {

		/* Pretend that the read succeeded and returned 0. */

include/linux/once_lite.h

+16 −4
Original line number Diff line number Diff line
@@ -9,15 +9,27 @@ 
 */

#define DO_ONCE_LITE(func, ...)						\

	DO_ONCE_LITE_IF(true, func, ##__VA_ARGS__)

#define DO_ONCE_LITE_IF(condition, func, ...)				\



#define __ONCE_LITE_IF(condition)					\

	({								\

		static bool __section(".data.once") __already_done;	\

		bool __ret_do_once = !!(condition);			\

		bool __ret_cond = !!(condition);			\

		bool __ret_once = false;				\

									\

		if (unlikely(__ret_do_once && !__already_done)) {	\

		if (unlikely(__ret_cond && !__already_done)) {		\

			__already_done = true;				\

			func(__VA_ARGS__);				\

			__ret_once = true;				\

		}							\

		unlikely(__ret_once);					\

	})



#define DO_ONCE_LITE_IF(condition, func, ...)				\

	({								\

		bool __ret_do_once = !!(condition);			\

									\

		if (__ONCE_LITE_IF(__ret_do_once))			\

			func(__VA_ARGS__);				\

									\

		unlikely(__ret_do_once);				\

	})