[PATCH AUTOSEL 4.9 05/74] ARM: prevent tracing IPI_CPU_BACKTRACE

[Sasha Levin]

From: Arnd Bergmann <arnd@xxxxxxxx>

[ Upstream commit be167862ae7dd85c56d385209a4890678e1b0488 ]

Patch series "compiler: allow all arches to enable
CONFIG_OPTIMIZE_INLINING", v3.

This patch (of 11):

When function tracing for IPIs is enabled, we get a warning for an
overflow of the ipi_types array with the IPI_CPU_BACKTRACE type as
triggered by raise_nmi():

  arch/arm/kernel/smp.c: In function 'raise_nmi':
  arch/arm/kernel/smp.c:489:2: error: array subscript is above array bounds [-Werror=array-bounds]
    trace_ipi_raise(target, ipi_types[ipinr]);

This is a correct warning as we actually overflow the array here.

This patch raise_nmi() to call __smp_cross_call() instead of
smp_cross_call(), to avoid calling into ftrace.  For clarification, I'm
also adding a two new code comments describing how this one is special.

The warning appears to have shown up after commit e7273ff49acf ("ARM:
8488/1: Make IPI_CPU_BACKTRACE a "non-secure" SGI"), which changed the
number assignment from '15' to '8', but as far as I can tell has existed
since the IPI tracepoints were first introduced.  If we decide to
backport this patch to stable kernels, we probably need to backport
e7273ff49acf as well.

[yamada.masahiro@xxxxxxxxxxxxx: rebase on v5.1-rc1]
Link: http://lkml.kernel.org/r/20190423034959.13525-2-yamada.masahiro@xxxxxxxxxxxxx
Fixes: e7273ff49acf ("ARM: 8488/1: Make IPI_CPU_BACKTRACE a "non-secure" SGI")
Fixes: 365ec7b17327 ("ARM: add IPI tracepoints") # v3.17
Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
Signed-off-by: Masahiro Yamada <yamada.masahiro@xxxxxxxxxxxxx>
Cc: Heiko Carstens <heiko.carstens@xxxxxxxxxx>
Cc: Arnd Bergmann <arnd@xxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Christophe Leroy <christophe.leroy@xxxxxx>
Cc: Mathieu Malaterre <malat@xxxxxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>
Cc: Paul Mackerras <paulus@xxxxxxxxx>
Cc: Ralf Baechle <ralf@xxxxxxxxxxxxxx>
Cc: Stefan Agner <stefan@xxxxxxxx>
Cc: Boris Brezillon <bbrezillon@xxxxxxxxxx>
Cc: Miquel Raynal <miquel.raynal@xxxxxxxxxxx>
Cc: Richard Weinberger <richard@xxxxxx>
Cc: David Woodhouse <dwmw2@xxxxxxxxxxxxx>
Cc: Brian Norris <computersforpeace@xxxxxxxxx>
Cc: Marek Vasut <marek.vasut@xxxxxxxxx>
Cc: Russell King <rmk+kernel@xxxxxxxxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxx>
Cc: Mark Rutland <mark.rutland@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 arch/arm/include/asm/hardirq.h | 1 +
 arch/arm/kernel/smp.c          | 6 +++++-
 2 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/arch/arm/include/asm/hardirq.h b/arch/arm/include/asm/hardirq.h
index 3d7351c844aac..2fd0a2619b0b3 100644
--- a/arch/arm/include/asm/hardirq.h
+++ b/arch/arm/include/asm/hardirq.h
@@ -5,6 +5,7 @@
 #include <linux/threads.h>
 #include <asm/irq.h>
 
+/* number of IPIS _not_ including IPI_CPU_BACKTRACE */
 #define NR_IPI	7
 
 typedef struct {
diff --git a/arch/arm/kernel/smp.c b/arch/arm/kernel/smp.c
index 7a5dc011c5230..deea60f01d245 100644
--- a/arch/arm/kernel/smp.c
+++ b/arch/arm/kernel/smp.c
@@ -75,6 +75,10 @@ enum ipi_msg_type {
 	IPI_CPU_STOP,
 	IPI_IRQ_WORK,
 	IPI_COMPLETION,
+	/*
+	 * CPU_BACKTRACE is special and not included in NR_IPI
+	 * or tracable with trace_ipi_*
+	 */
 	IPI_CPU_BACKTRACE,
 	/*
 	 * SGI8-15 can be reserved by secure firmware, and thus may
@@ -801,7 +805,7 @@ core_initcall(register_cpufreq_notifier);
 
 static void raise_nmi(cpumask_t *mask)
 {
-	smp_cross_call(mask, IPI_CPU_BACKTRACE);
+	__smp_cross_call(mask, IPI_CPU_BACKTRACE);
 }
 
 void arch_trigger_cpumask_backtrace(const cpumask_t *mask, bool exclude_self)
-- 
2.20.1