[RFC PATCH 5/9] x86/um/vdso: nommu: vdso memory update

[Johannes Berg]

From: Hajime Tazaki <thehajime at gmail.com>

On !MMU mode, the address of vdso is accessible from userspace.  This
commit implements the entry point by pointing a block of page address.

This commit also add memory permission configuration of vdso page to be
executable.

Signed-off-by: Hajime Tazaki <thehajime at gmail.com>
Signed-off-by: Ricardo Koller <ricarkol at google.com>
Link: https://patch.msgid.link/1779dfb80f0e6fc25c001062a1e00cb661531c23.1770170302.git.thehajime@gmail.com
[remove print, add comment on #endif]
Signed-off-by: Johannes Berg <johannes.berg at intel.com>
---
 arch/x86/um/vdso/vma.c | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/arch/x86/um/vdso/vma.c b/arch/x86/um/vdso/vma.c
index 51a2b9f2eca9..8e1f5ee44f4e 100644
--- a/arch/x86/um/vdso/vma.c
+++ b/arch/x86/um/vdso/vma.c
@@ -9,6 +9,7 @@
 #include <asm/page.h>
 #include <asm/elf.h>
 #include <linux/init.h>
+#include <os.h>
 
 unsigned long um_vdso_addr;
 static struct page *um_vdso;
@@ -20,18 +21,25 @@ static int __init init_vdso(void)
 {
 	BUG_ON(vdso_end - vdso_start > PAGE_SIZE);
 
-	um_vdso_addr = task_size - PAGE_SIZE;
-
 	um_vdso = alloc_page(GFP_KERNEL);
 	if (!um_vdso)
 		panic("Cannot allocate vdso\n");
 
 	copy_page(page_address(um_vdso), vdso_start);
 
+#ifdef CONFIG_MMU
+	um_vdso_addr = task_size - PAGE_SIZE;
+#else
+	/* this is fine with NOMMU as everything is accessible */
+	um_vdso_addr = (unsigned long)page_address(um_vdso);
+	os_protect_memory((void *)um_vdso_addr, vdso_end - vdso_start, 1, 0, 1);
+#endif
+
 	return 0;
 }
 subsys_initcall(init_vdso);
 
+#ifdef CONFIG_MMU
 int arch_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)
 {
 	struct vm_area_struct *vma;
@@ -53,3 +61,4 @@ int arch_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)
 
 	return IS_ERR(vma) ? PTR_ERR(vma) : 0;
 }
+#endif /* CONFIG_MMU */
-- 
2.53.0