[xen staging] x86: verify function type (and maybe attribute) in switch_stack_and_jump()

[patchbot@xxxxxxx]

commit 1a050d69faffe42fd22dbe9c9c49e2228919148f
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Tue Dec 22 08:57:19 2020 +0100
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Tue Dec 22 08:57:19 2020 +0100

    x86: verify function type (and maybe attribute) in switch_stack_and_jump()
    
    It is imperative that the functions passed here are taking no arguments,
    return no values, and don't return in the first place. While the type
    can be checked uniformly, the attribute check is limited to gcc 9 and
    newer (no clang support for this so far afaict).
    
    Note that I didn't want to have the "true" fallback "implementation" of
    __builtin_has_attribute(..., __noreturn__) generally available, as
    "true" may not be a suitable fallback in other cases.
    
    Note further that the noreturn addition to startup_cpu_idle_loop()'s
    declaration requires adding unreachable() to Arm's
    switch_stack_and_jump(), or else the build would break. I suppose this
    should have been there already.
    
    For vmx_asm_do_vmentry() along with adding the attribute, also restrict
    its scope.
    
    Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
    Reviewed-by: Juergen Gross <jgross@xxxxxxxx>
    Reviewed-by: Wei Liu <wl@xxxxxxx>
    Acked-by: Julien Grall <jgrall@xxxxxxxxxx>
---
 xen/arch/x86/hvm/svm/svm.c        | 2 +-
 xen/arch/x86/hvm/vmx/vmcs.c       | 2 ++
 xen/arch/x86/setup.c              | 2 +-
 xen/include/asm-arm/current.h     | 6 ++++--
 xen/include/asm-x86/current.h     | 9 +++++++++
 xen/include/asm-x86/hvm/vmx/vmx.h | 1 -
 xen/include/xen/sched.h           | 2 +-
 7 files changed, 18 insertions(+), 6 deletions(-)

diff --git a/xen/arch/x86/hvm/svm/svm.c b/xen/arch/x86/hvm/svm/svm.c
index d90627d4f7..0854fcfc14 100644
--- a/xen/arch/x86/hvm/svm/svm.c
+++ b/xen/arch/x86/hvm/svm/svm.c
@@ -63,7 +63,7 @@
 #include <asm/monitor.h>
 #include <asm/xstate.h>
 
-void svm_asm_do_resume(void);
+void noreturn svm_asm_do_resume(void);
 
 u32 svm_feature_flags;
 
diff --git a/xen/arch/x86/hvm/vmx/vmcs.c b/xen/arch/x86/hvm/vmx/vmcs.c
index 1466064d0c..164535f8f0 100644
--- a/xen/arch/x86/hvm/vmx/vmcs.c
+++ b/xen/arch/x86/hvm/vmx/vmcs.c
@@ -1850,6 +1850,8 @@ void vmx_vmentry_failure(void)
     domain_crash(curr->domain);
 }
 
+void noreturn vmx_asm_do_vmentry(void);
+
 void vmx_do_resume(void)
 {
     struct vcpu *v = current;
diff --git a/xen/arch/x86/setup.c b/xen/arch/x86/setup.c
index 1a2e5e41ab..5cdb0f0f92 100644
--- a/xen/arch/x86/setup.c
+++ b/xen/arch/x86/setup.c
@@ -619,7 +619,7 @@ static inline bool using_2M_mapping(void)
            !l1_table_offset((unsigned long)__2M_rwdata_end);
 }
 
-static void noinline init_done(void)
+static void noreturn init_done(void)
 {
     void *va;
     unsigned long start, end;
diff --git a/xen/include/asm-arm/current.h b/xen/include/asm-arm/current.h
index f71da9fab9..e7fbf535d2 100644
--- a/xen/include/asm-arm/current.h
+++ b/xen/include/asm-arm/current.h
@@ -43,8 +43,10 @@ static inline struct cpu_info *get_cpu_info(void)
 
 #define guest_cpu_user_regs() (&get_cpu_info()->guest_cpu_user_regs)
 
-#define switch_stack_and_jump(stack, fn)                                \
-    asm volatile ("mov sp,%0; b " STR(fn) : : "r" (stack) : "memory" )
+#define switch_stack_and_jump(stack, fn) do {                           \
+    asm volatile ("mov sp,%0; b " STR(fn) : : "r" (stack) : "memory" ); \
+    unreachable();                                                      \
+} while ( false )
 
 #define reset_stack_and_jump(fn) switch_stack_and_jump(get_cpu_info(), fn)
 
diff --git a/xen/include/asm-x86/current.h b/xen/include/asm-x86/current.h
index 231994a245..5d690ce014 100644
--- a/xen/include/asm-x86/current.h
+++ b/xen/include/asm-x86/current.h
@@ -163,9 +163,18 @@ unsigned long get_stack_dump_bottom (unsigned long sp);
 # define SHADOW_STACK_WORK ""
 #endif
 
+#if __GNUC__ >= 9
+# define ssaj_has_attr_noreturn(fn) __builtin_has_attribute(fn, __noreturn__)
+#else
+/* Simply can't check the property with older gcc. */
+# define ssaj_has_attr_noreturn(fn) true
+#endif
+
 #define switch_stack_and_jump(fn, instr, constr)                        \
     ({                                                                  \
         unsigned int tmp;                                               \
+        (void)((fn) == (void (*)(void))NULL);                           \
+        BUILD_BUG_ON(!ssaj_has_attr_noreturn(fn));                      \
         __asm__ __volatile__ (                                          \
             SHADOW_STACK_WORK                                           \
             "mov %[stk], %%rsp;"                                        \
diff --git a/xen/include/asm-x86/hvm/vmx/vmx.h 
b/xen/include/asm-x86/hvm/vmx/vmx.h
index 09ea0fa2cd..534e9fc221 100644
--- a/xen/include/asm-x86/hvm/vmx/vmx.h
+++ b/xen/include/asm-x86/hvm/vmx/vmx.h
@@ -93,7 +93,6 @@ typedef enum {
 #define PI_xAPIC_NDST_MASK      0xFF00
 
 void vmx_asm_vmexit_handler(struct cpu_user_regs);
-void vmx_asm_do_vmentry(void);
 void vmx_intr_assist(void);
 void noreturn vmx_do_resume(void);
 void vmx_vlapic_msr_changed(struct vcpu *v);
diff --git a/xen/include/xen/sched.h b/xen/include/xen/sched.h
index faf5fda36f..76af29e932 100644
--- a/xen/include/xen/sched.h
+++ b/xen/include/xen/sched.h
@@ -736,7 +736,7 @@ void sched_context_switched(struct vcpu *prev, struct vcpu 
*vnext);
 void continue_running(
     struct vcpu *same);
 
-void startup_cpu_idle_loop(void);
+void noreturn startup_cpu_idle_loop(void);
 extern void (*pm_idle) (void);
 extern void (*dead_idle) (void);
 
--
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