lkml.org 
[lkml]   [2022]   [Jul]   [21]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
Subject[tip: x86/core] x86/extable: Fix ex_handler_msr() print condition
The following commit has been merged into the x86/core branch of tip:

Commit-ID: a1a5482a2c6e38a3ebed32e571625c56a8cc41a6
Gitweb: https://git.kernel.org/tip/a1a5482a2c6e38a3ebed32e571625c56a8cc41a6
Author: Peter Zijlstra <peterz@infradead.org>
AuthorDate: Fri, 17 Jun 2022 16:52:06 +02:00
Committer: Peter Zijlstra <peterz@infradead.org>
CommitterDate: Thu, 21 Jul 2022 10:39:42 +02:00

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):
>
> a358f40600b3 ("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: a358f40600b3 ("once: implement DO_ONCE_LITE for non-fast-path "do once" functionality")
Reported-by: Stephane Eranian <eranian@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Stephane Eranian <eranian@google.com>
Link: https://lkml.kernel.org/r/YqyVFsbviKjVGGZ9@worktop.programming.kicks-ass.net
---
arch/x86/mm/extable.c | 16 +++++++++-------
include/linux/once_lite.h | 20 ++++++++++++++++----
2 files changed, 25 insertions(+), 11 deletions(-)

diff --git a/arch/x86/mm/extable.c b/arch/x86/mm/extable.c
index dba2197..331310c 100644
--- a/arch/x86/mm/extable.c
+++ b/arch/x86/mm/extable.c
@@ -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",
- (unsigned int)regs->cx, (unsigned int)regs->dx,
- (unsigned int)regs->ax, regs->ip, (void *)regs->ip))
+ 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);
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. */
diff --git a/include/linux/once_lite.h b/include/linux/once_lite.h
index 861e606..b7bce49 100644
--- a/include/linux/once_lite.h
+++ b/include/linux/once_lite.h
@@ -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); \
})

\
 
 \ /
  Last update: 2022-07-21 10:53    [W:1.124 / U:0.108 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site