linux-kernel - [PATCH] x86/xen: Remove undefined behavior in setup

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Date:   Fri, 17 Jun 2022 11:30:37 +0100
From:   Julien Grall <julien@....org>
To:     xen-devel@...ts.xenproject.org
Cc:     sstabellini@...nel.org, jgross@...e.com,
        oleksandr_tyshchenko@...m.com, linux-kernel@...r.kernel.org,
        Julien Grall <jgrall@...zon.com>
Subject: [PATCH] x86/xen: Remove undefined behavior in setup_features()

From: Julien Grall <jgrall@...zon.com>

1 << 31 is undefined. So switch to 1U << 31.

Fixes: 5ead97c84fa7 ("xen: Core Xen implementation")
Signed-off-by: Julien Grall <jgrall@...zon.com>

---

This was actually caught because I wasn't able to boot Linux 5.18
and onwards when built with GCC 7.3 and UBSAN enabled. There was
no message but instead an early crash because the instruction "cli
was used too early.

This issue has always been there but it only shows after Linux
switched from C89 to C11.
---
 drivers/xen/features.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/xen/features.c b/drivers/xen/features.c
index 7b591443833c..87f1828d40d5 100644
--- a/drivers/xen/features.c
+++ b/drivers/xen/features.c
@@ -42,7 +42,7 @@ void xen_setup_features(void)
 		if (HYPERVISOR_xen_version(XENVER_get_features, &fi) < 0)
 			break;
 		for (j = 0; j < 32; j++)
-			xen_features[i * 32 + j] = !!(fi.submap & 1<<j);
+			xen_features[i * 32 + j] = !!(fi.submap & 1U << j);
 	}
 
 	if (xen_pv_domain()) {
-- 
2.32.0