arm64: compat: Get sigreturn trampolines from vDSO

When the compat vDSO is enabled, the sigreturn trampolines are not
anymore available through [sigpage] but through [vdso].

Add the relevant code the enable the feature.

Signed-off-by: Vincenzo Frascino <[e-mail]>
Signed-off-by: Thomas Gleixner <[e-mail]>
Tested-by: Shijith Thotton <[e-mail]>
Tested-by: Andre Przywara <[e-mail]>
Cc: [e-mail]
Cc: [e-mail]
Cc: [e-mail]
Cc: [e-mail]
Cc: Catalin Marinas <[e-mail]>
Cc: Will Deacon <[e-mail]>
Cc: Arnd Bergmann <[e-mail]>
Cc: Russell King <[e-mail]>
Cc: Ralf Baechle <[e-mail]>
Cc: Paul Burton <[e-mail]>
Cc: Daniel Lezcano <[e-mail]>
Cc: Mark Salyzyn <[e-mail]>
Cc: Peter Collingbourne <[e-mail]>
Cc: Shuah Khan <[e-mail]>
Cc: Dmitry Safonov <[e-mail]>
Cc: Rasmus Villemoes <[e-mail]>
Cc: Huw Davies <[e-mail]>
Link: https://lkml.kernel.org/r/[e-mail]

arch/arm64/include/asm/vdso.h

···
 #ifndef __ASSEMBLY__
 
 #include <generated/vdso-offsets.h>
+#ifdef CONFIG_COMPAT_VDSO
+#include <generated/vdso32-offsets.h>
+#endif
 
 #define VDSO_SYMBOL(base, name)						   \
 ({									   \

arch/arm64/kernel/signal32.c

···
 #include <asm/traps.h>
 #include <linux/uaccess.h>
 #include <asm/unistd.h>
+#include <asm/vdso.h>
 
 struct compat_vfp_sigframe {
 	compat_ulong_t	magic;
···
 		retcode = ptr_to_compat(ka->sa.sa_restorer);
 	} else {
 		/* Set up sigreturn pointer */
+#ifdef CONFIG_COMPAT_VDSO
+		void *vdso_base = current->mm->context.vdso;
+		void *vdso_trampoline;
+
+		if (ka->sa.sa_flags & SA_SIGINFO) {
+			if (thumb) {
+				vdso_trampoline = VDSO_SYMBOL(vdso_base,
+							compat_rt_sigreturn_thumb);
+			} else {
+				vdso_trampoline = VDSO_SYMBOL(vdso_base,
+							compat_rt_sigreturn_arm);
+			}
+		} else {
+			if (thumb) {
+				vdso_trampoline = VDSO_SYMBOL(vdso_base,
+							compat_sigreturn_thumb);
+			} else {
+				vdso_trampoline = VDSO_SYMBOL(vdso_base,
+							compat_sigreturn_arm);
+			}
+		}
+
+		retcode = ptr_to_compat(vdso_trampoline) + thumb;
+#else
 		unsigned int idx = thumb << 1;
 
 		if (ka->sa.sa_flags & SA_SIGINFO)
···
 
 		retcode = (unsigned long)current->mm->context.vdso +
 			  (idx << 2) + thumb;
+#endif
 	}
 
 	regs->regs[0]	= usig;