[PATCH v7 4/6] panic: restore variable arguments to nmi_panic()

[Bradley Morgan <brads@mainlining.org>]

nmi_panic() used to accept variable arguments until commit
ebc41f20d77f ("panic: change nmi_panic from macro to function")
flattened it to a final message string. vpanic() did not exist back
then, so the function had to format through panic("%s", msg).

Bring the variable arguments back and format with vpanic() directly.
The next patch makes nmi_panic() try the panic_force_cpu= redirect
before claiming panic_cpu, which needs the arguments twice: once to
format the message for the redirected CPU and once for vpanic() when
no redirect happens. Passing a final string would lose that.

No current caller passes a string with format specifiers. The closest
one is hpwdt_pretimeout(), which builds panic_msg with hex_byte_pack()
and has only two variants, both plain strings. But the new __printf()
annotation on nmi_panic() would warn with -Wformat-security there
because the buffer is passed directly as the format argument, so
switch it to nmi_panic(regs, "%s", panic_msg).

Suggested-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Bradley Morgan <brads@mainlining.org>
---
 drivers/watchdog/hpwdt.c |  2 +-
 include/linux/panic.h    |  3 ++-
 kernel/panic.c           | 10 ++++++++--
 3 files changed, 11 insertions(+), 4 deletions(-)

diff --git a/drivers/watchdog/hpwdt.c b/drivers/watchdog/hpwdt.c
index 8af1fad2de0b..78227d200afe 100644
--- a/drivers/watchdog/hpwdt.c
+++ b/drivers/watchdog/hpwdt.c
@@ -199,7 +199,7 @@ static int hpwdt_pretimeout(unsigned int ulReason, struct pt_regs *regs)
 	}
 
 	hex_byte_pack(panic_msg, nmistat);
-	nmi_panic(regs, panic_msg);
+	nmi_panic(regs, "%s", panic_msg);
 
 	return NMI_HANDLED;
 }
diff --git a/include/linux/panic.h b/include/linux/panic.h
index 98dd7dfd27de..17e61b61c45f 100644
--- a/include/linux/panic.h
+++ b/include/linux/panic.h
@@ -13,7 +13,8 @@ __printf(1, 2)
 void panic(const char *fmt, ...) __noreturn __cold;
 __printf(1, 0)
 void vpanic(const char *fmt, va_list args) __noreturn __cold;
-void nmi_panic(struct pt_regs *regs, const char *msg);
+__printf(2, 3)
+void nmi_panic(struct pt_regs *regs, const char *fmt, ...);
 void check_panic_on_warn(const char *origin);
 extern void oops_enter(void);
 extern void oops_exit(void);
diff --git a/kernel/panic.c b/kernel/panic.c
index 7388eb81a1c4..e240ca06faab 100644
--- a/kernel/panic.c
+++ b/kernel/panic.c
@@ -518,13 +518,19 @@ EXPORT_SYMBOL(panic_on_other_cpu);
  * nmi_panic_self_stop() which can provide architecture dependent code such
  * as saving register state for crash dump.
  */
-void nmi_panic(struct pt_regs *regs, const char *msg)
+void nmi_panic(struct pt_regs *regs, const char *fmt, ...)
 {
+	va_list args;
+
+	va_start(args, fmt);
+
 	if (panic_try_start())
-		panic("%s", msg);
+		vpanic(fmt, args);
 
 	if (panic_on_other_cpu())
 		nmi_panic_self_stop(regs);
+
+	va_end(args);
 }
 EXPORT_SYMBOL(nmi_panic);
 
-- 
2.47.3