blob: 3c36d489df0ea64ba57b22d2e266b7d9ed642a7e [file] [log] [blame]
From b0301cc009dcb271a55b0b7598554b90fa86baf8 Mon Sep 17 00:00:00 2001
From: Kees Cook <>
Date: Wed, 19 Feb 2020 22:23:18 -0800
Subject: [PATCH] x86/xen: Distribute switch variables for initialization
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commit 9038ec99ceb94fb8d93ade5e236b2928f0792c7c upstream.
Variables declared in a switch statement before any case statements
cannot be automatically initialized with compiler instrumentation (as
they are not part of any execution flow). With GCC's proposed automatic
stack variable initialization feature, this triggers a warning (and they
don't get initialized). Clang's automatic stack variable initialization
(via CONFIG_INIT_STACK_ALL=y) doesn't throw a warning, but it also
doesn't initialize such variables[1]. Note that these warnings (or silent
skipping) happen before the dead-store elimination optimization phase,
so even when the automatic initializations are later elided in favor of
direct initializations, the warnings remain.
To avoid these problems, move such variables into the "case" where
they're used or lift them up into the main function body.
arch/x86/xen/enlighten_pv.c: In function xen_write_msr_safe’:
arch/x86/xen/enlighten_pv.c:904:12: warning: statement will never be executed [-Wswitch-unreachable]
904 | unsigned which;
| ^~~~~
Signed-off-by: Kees Cook <>
Reviewed-by: Juergen Gross <>
[boris: made @which an 'unsigned int']
Signed-off-by: Boris Ostrovsky <>
Signed-off-by: Paul Gortmaker <>
diff --git a/arch/x86/xen/enlighten_pv.c b/arch/x86/xen/enlighten_pv.c
index 896cfd22cfda..c9b51e1a0c53 100644
--- a/arch/x86/xen/enlighten_pv.c
+++ b/arch/x86/xen/enlighten_pv.c
@@ -907,14 +907,15 @@ static u64 xen_read_msr_safe(unsigned int msr, int *err)
static int xen_write_msr_safe(unsigned int msr, unsigned low, unsigned high)
int ret;
+#ifdef CONFIG_X86_64
+ unsigned int which;
+ u64 base;
ret = 0;
switch (msr) {
#ifdef CONFIG_X86_64
- unsigned which;
- u64 base;
case MSR_FS_BASE: which = SEGBASE_FS; goto set;
case MSR_KERNEL_GS_BASE: which = SEGBASE_GS_USER; goto set;
case MSR_GS_BASE: which = SEGBASE_GS_KERNEL; goto set;