From 297435d902e2f6ebea6de3320c688bef7a744adc 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 MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit [ Upstream commit 9038ec99ceb94fb8d93ade5e236b2928f0792c7c ] 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; | ^~~~~ [1] https://bugs.llvm.org/show_bug.cgi?id=44916 Signed-off-by: Kees Cook Link: https://lore.kernel.org/r/20200220062318.69299-1-keescook@chromium.org Reviewed-by: Juergen Gross [boris: made @which an 'unsigned int'] Signed-off-by: Boris Ostrovsky Signed-off-by: Sasha Levin --- arch/x86/xen/enlighten_pv.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) diff --git a/arch/x86/xen/enlighten_pv.c b/arch/x86/xen/enlighten_pv.c index 1730a26..76864ea 100644 --- a/arch/x86/xen/enlighten_pv.c +++ b/arch/x86/xen/enlighten_pv.c @@ -908,14 +908,15 @@ 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; +#endif 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; -- 2.7.4