[PATCH 16/19] arm/vdso: Migrate to user_landing

[Dmitry Safonov <dima@arista.com>]

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

Signed-off-by: Dmitry Safonov <dima@arista.com>
---
 arch/arm/Kconfig          | 1 +
 arch/arm/kernel/process.c | 9 +--------
 arch/arm/kernel/signal.c  | 6 +++++-
 3 files changed, 7 insertions(+), 9 deletions(-)

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index bece41f3b3b9..c161d7313911 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -24,6 +24,7 @@ config ARM
 	select ARCH_HAS_SYNC_DMA_FOR_CPU if SWIOTLB
 	select ARCH_HAS_TEARDOWN_DMA_OPS if MMU
 	select ARCH_HAS_TICK_BROADCAST if GENERIC_CLOCKEVENTS_BROADCAST
+	select ARCH_HAS_USER_LANDING
 	select ARCH_HAVE_CUSTOM_GPIO_H
 	select ARCH_HAS_GCOV_PROFILE_ALL
 	select ARCH_KEEP_MEMBLOCK
diff --git a/arch/arm/kernel/process.c b/arch/arm/kernel/process.c
index 5f4eced738f5..ac08241e5cf8 100644
--- a/arch/arm/kernel/process.c
+++ b/arch/arm/kernel/process.c
@@ -376,16 +376,9 @@ static unsigned long sigpage_addr(const struct mm_struct *mm,
 static struct page *signal_page;
 extern struct page *get_signal_page(void);
 
-static void sigpage_mremap(const struct vm_special_mapping *sm,
-		struct vm_area_struct *new_vma)
-{
-	current->mm->context.sigpage = new_vma->vm_start;
-}
-
 static const struct vm_special_mapping sigpage_mapping = {
 	.name = "[sigpage]",
 	.pages = &signal_page,
-	.mremap = sigpage_mremap,
 };
 
 int arch_setup_additional_pages(unsigned long *sysinfo_ehdr)
@@ -423,7 +416,7 @@ int arch_setup_additional_pages(unsigned long *sysinfo_ehdr)
 		goto up_fail;
 	}
 
-	mm->context.sigpage = addr;
+	mm->user_landing = (void __user *)addr;
 
 	/* Unlike the sigpage, failure to install the vdso is unlikely
 	 * to be fatal to the process, so no error check needed
diff --git a/arch/arm/kernel/signal.c b/arch/arm/kernel/signal.c
index 9d2e916121be..270b17a9dc0f 100644
--- a/arch/arm/kernel/signal.c
+++ b/arch/arm/kernel/signal.c
@@ -451,13 +451,17 @@ setup_return(struct pt_regs *regs, struct ksignal *ksig,
 #ifdef CONFIG_MMU
 		if (cpsr & MODE32_BIT) {
 			struct mm_struct *mm = current->mm;
+			unsigned long land = (unsigned long)mm->user_landing;
+
+			if (land == UNMAPPED_USER_LANDING)
+				return 1;
 
 			/*
 			 * 32-bit code can use the signal return page
 			 * except when the MPU has protected the vectors
 			 * page from PL0
 			 */
-			retcode = mm->context.sigpage + signal_return_offset +
+			retcode = land + signal_return_offset +
 				  (idx << 2) + thumb;
 		} else
 #endif
-- 
2.28.0