mips/vdso: Migrate to user_landing

Generic way to track the land vma area.
As a bonus, after unmapping sigpage, kernel won't try to land on its
previous position.

Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Cc: linux-mips@vger.kernel.org
Signed-off-by: Dmitry Safonov <dima@arista.com>

arch/mips/Kconfig

@@ -10,6 +10,7 @@ config MIPS
 	select ARCH_HAS_SETUP_ADDITIONAL_PAGES
 	select ARCH_HAS_TICK_BROADCAST if GENERIC_CLOCKEVENTS_BROADCAST
 	select ARCH_HAS_UBSAN_SANITIZE_ALL
+	select ARCH_HAS_USER_LANDING
 	select ARCH_SUPPORTS_UPROBES
 	select ARCH_USE_BUILTIN_BSWAP
 	select ARCH_USE_CMPXCHG_LOCKREF if 64BIT

arch/mips/kernel/signal.c

@@ -806,11 +806,13 @@ struct mips_abi mips_abi = {
 
 static void handle_signal(struct ksignal *ksig, struct pt_regs *regs)
 {
+	unsigned long land = (unsigned long)current->mm->user_landing;
 	sigset_t *oldset = sigmask_to_save();
-	int ret;
+	int ret = 1;
 	struct mips_abi *abi = current->thread.abi;
-	void *vdso = current->mm->context.vdso;
 
+	if (land == UNMAPPED_USER_LANDING)
+		goto err;
 	/*
 	 * If we were emulating a delay slot instruction, exit that frame such
 	 * that addresses in the sigframe are as expected for userland and we
@@ -843,12 +845,13 @@ static void handle_signal(struct ksignal *ksig, struct pt_regs *regs)
 	rseq_signal_deliver(ksig, regs);
 
 	if (sig_uses_siginfo(&ksig->ka, abi))
-		ret = abi->setup_rt_frame(vdso + abi->vdso->off_rt_sigreturn,
+		ret = abi->setup_rt_frame(land + abi->vdso->off_rt_sigreturn,
 					  ksig, regs, oldset);
 	else
-		ret = abi->setup_frame(vdso + abi->vdso->off_sigreturn,
+		ret = abi->setup_frame(land + abi->vdso->off_sigreturn,
 				       ksig, regs, oldset);
 
+err:
 	signal_setup_done(ret, ksig, 0);
 }
 

arch/mips/kernel/vdso.c

@@ -183,7 +183,7 @@ int arch_setup_additional_pages(unsigned long *sysinfo_ehdr)
 		goto out;
 	}
 
-	mm->context.vdso = (void *)vdso_addr;
+	mm->user_landing = (void __user *)vdso_addr;
 	*sysinfo_ehdr = vdso_addr;
 	ret = 0;
 

arch/mips/vdso/genvdso.c

@@ -259,13 +259,6 @@ int main(int argc, char **argv)
 	fprintf(out_file, "#include <linux/linkage.h>\n");
 	fprintf(out_file, "#include <linux/mm.h>\n");
 	fprintf(out_file, "#include <asm/vdso.h>\n");
-	fprintf(out_file, "static void vdso_mremap(\n");
-	fprintf(out_file, "	const struct vm_special_mapping *sm,\n");
-	fprintf(out_file, "	struct vm_area_struct *new_vma)\n");
-	fprintf(out_file, "{\n");
-	fprintf(out_file, "	current->mm->context.vdso =\n");
-	fprintf(out_file, "	(void *)(new_vma->vm_start);\n");
-	fprintf(out_file, "}\n");
 
 	/* Write out the stripped VDSO data. */
 	fprintf(out_file,
@@ -290,7 +283,6 @@ int main(int argc, char **argv)
 	fprintf(out_file, "\t.mapping = {\n");
 	fprintf(out_file, "\t\t.name = \"[vdso]\",\n");
 	fprintf(out_file, "\t\t.pages = vdso_pages,\n");
-	fprintf(out_file, "\t\t.mremap = vdso_mremap,\n");
 	fprintf(out_file, "\t},\n");
 
 	/* Calculate and write symbol offsets to <output file> */