linux-hardening - [PATCH] printk: add cpu id information to printk() output

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Date:   Fri, 15 Sep 2023 15:40:34 +0800
From:   Enlin Mu <enlin.mu@...look.com>
To:     pmladek@...e.com, rostedt@...dmis.org, john.ogness@...utronix.de,
        senozhatsky@...omium.org, keescook@...omium.org,
        tony.luck@...el.com, gpiccoli@...lia.com, enlin.mu@...soc.com,
        enlinmu@...il.com
Cc:     linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: [PATCH] printk: add cpu id information to printk() output

From: Enlin Mu <enlin.mu@...soc.com>

Sometimes we want to print cpu id of printk() messages to consoles

Signed-off-by: Enlin Mu <enlin.mu@...soc.com>
---
 include/linux/threads.h |  3 +++
 kernel/printk/printk.c  | 18 +++++++++++++-----
 2 files changed, 16 insertions(+), 5 deletions(-)

diff --git a/include/linux/threads.h b/include/linux/threads.h
index c34173e6c5f1..6700bd9a174f 100644
--- a/include/linux/threads.h
+++ b/include/linux/threads.h
@@ -34,6 +34,9 @@
 #define PID_MAX_LIMIT (CONFIG_BASE_SMALL ? PAGE_SIZE * 8 : \
 	(sizeof(long) > 4 ? 4 * 1024 * 1024 : PID_MAX_DEFAULT))
 
+#define CPU_ID_SHIFT 23
+#define CPU_ID_MASK  0xff800000
+
 /*
  * Define a minimum number of pids per cpu.  Heuristically based
  * on original pid max of 32k for 32 cpus.  Also, increase the
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 7e0b4dd02398..f3f3ca89b251 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -629,8 +629,12 @@ static ssize_t info_print_ext_header(char *buf, size_t size,
 #ifdef CONFIG_PRINTK_CALLER
 	u32 id = info->caller_id;
 
-	snprintf(caller, sizeof(caller), ",caller=%c%u",
-		 id & 0x80000000 ? 'C' : 'T', id & ~0x80000000);
+	if (id&0x80000000)
+		snprintf(caller, sizeof(caller), ",caller=C%u",
+			id & ~0x80000000);
+	else
+		snprintf(caller, sizeof(caller), ",caller=T%uC%u",
+			id & ~CPU_ID_MASK, id >> CPU_ID_SHIFT);
 #else
 	caller[0] = '\0';
 #endif
@@ -1333,8 +1337,12 @@ static size_t print_caller(u32 id, char *buf)
 {
 	char caller[12];
 
-	snprintf(caller, sizeof(caller), "%c%u",
-		 id & 0x80000000 ? 'C' : 'T', id & ~0x80000000);
+	if (id & 0x80000000)
+		snprintf(caller, sizeof(caller), "C%u",
+			id & ~0x80000000);
+	else
+		snprintf(caller, sizeof(caller), "T%uC%u",
+			id & ~CPU_ID_MASK, id >> CPU_ID_SHIFT);
 	return sprintf(buf, "[%6s]", caller);
 }
 #else
@@ -2069,7 +2077,7 @@ static inline void printk_delay(int level)
 
 static inline u32 printk_caller_id(void)
 {
-	return in_task() ? task_pid_nr(current) :
+	return in_task() ? task_pid_nr(current) | (smp_processor_id() << CPU_ID_SHIFT) :
 		0x80000000 + smp_processor_id();
 }
 
-- 
2.25.1