From: Kees Cook <keescook@chromium.org> To: Boris Ostrovsky <boris.ostrovsky@oracle.com>, Juergen Gross <jgross@suse.com> Cc: Alexander Potapenko <glider@google.com>, Kees Cook <keescook@chromium.org>, Stefano Stabellini <sstabellini@kernel.org>, xen-devel@lists.xenproject.org, linux-kernel@vger.kernel.org Subject: [PATCH] x86/xen: Distribute switch variables for initialization Date: Wed, 19 Feb 2020 22:23:18 -0800 [thread overview] Message-ID: <20200220062318.69299-1-keescook@chromium.org> (raw) 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 <keescook@chromium.org> --- 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 1f756ffffe8b..789dc12b7962 100644 --- a/arch/x86/xen/enlighten_pv.c +++ b/arch/x86/xen/enlighten_pv.c @@ -896,14 +896,15 @@ 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 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;
WARNING: multiple messages have this Message-ID (diff)
From: Kees Cook <keescook@chromium.org> To: Boris Ostrovsky <boris.ostrovsky@oracle.com>, Juergen Gross <jgross@suse.com> Cc: xen-devel@lists.xenproject.org, Stefano Stabellini <sstabellini@kernel.org>, Alexander Potapenko <glider@google.com>, Kees Cook <keescook@chromium.org>, linux-kernel@vger.kernel.org Subject: [Xen-devel] [PATCH] x86/xen: Distribute switch variables for initialization Date: Wed, 19 Feb 2020 22:23:18 -0800 [thread overview] Message-ID: <20200220062318.69299-1-keescook@chromium.org> (raw) 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 <keescook@chromium.org> --- 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 1f756ffffe8b..789dc12b7962 100644 --- a/arch/x86/xen/enlighten_pv.c +++ b/arch/x86/xen/enlighten_pv.c @@ -896,14 +896,15 @@ 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 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; _______________________________________________ Xen-devel mailing list Xen-devel@lists.xenproject.org https://lists.xenproject.org/mailman/listinfo/xen-devel
next reply other threads:[~2020-02-20 6:23 UTC|newest] Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top 2020-02-20 6:23 Kees Cook [this message] 2020-02-20 6:23 ` [Xen-devel] [PATCH] x86/xen: Distribute switch variables for initialization Kees Cook 2020-02-20 6:37 ` Jürgen Groß 2020-02-20 6:37 ` [Xen-devel] " Jürgen Groß 2020-02-20 16:33 ` Boris Ostrovsky 2020-02-20 16:33 ` [Xen-devel] " Boris Ostrovsky 2020-02-20 23:05 ` Kees Cook 2020-02-20 23:05 ` [Xen-devel] " Kees Cook
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