[RFC PATCH v2 09/13] x86/um/vdso: nommu: vdso memory update

[Hajime Tazaki]

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>
---
 arch/x86/um/vdso/um_vdso.c | 20 ++++++++++++++++++++
 arch/x86/um/vdso/vma.c     | 14 ++++++++++++++
 2 files changed, 34 insertions(+)

diff --git a/arch/x86/um/vdso/um_vdso.c b/arch/x86/um/vdso/um_vdso.c
index cbae2584124f..eff3e6641a0e 100644
--- a/arch/x86/um/vdso/um_vdso.c
+++ b/arch/x86/um/vdso/um_vdso.c
@@ -23,10 +23,17 @@ int __vdso_clock_gettime(clockid_t clock, struct __kernel_old_timespec *ts)
 {
 	long ret;
 
+#ifdef CONFIG_MMU
 	asm("syscall"
 		: "=a" (ret)
 		: "0" (__NR_clock_gettime), "D" (clock), "S" (ts)
 		: "rcx", "r11", "memory");
+#else
+	asm("call *%1"
+		: "=a" (ret)
+		: "0" ((unsigned long)__NR_clock_gettime), "D" (clock), "S" (ts)
+		: "rcx", "r11", "memory");
+#endif
 
 	return ret;
 }
@@ -37,10 +44,17 @@ int __vdso_gettimeofday(struct __kernel_old_timeval *tv, struct timezone *tz)
 {
 	long ret;
 
+#ifdef CONFIG_MMU
 	asm("syscall"
 		: "=a" (ret)
 		: "0" (__NR_gettimeofday), "D" (tv), "S" (tz)
 		: "rcx", "r11", "memory");
+#else
+	asm("call *%1"
+		: "=a" (ret)
+		: "0" ((unsigned long)__NR_gettimeofday), "D" (tv), "S" (tz)
+		: "rcx", "r11", "memory");
+#endif
 
 	return ret;
 }
@@ -51,9 +65,15 @@ __kernel_old_time_t __vdso_time(__kernel_old_time_t *t)
 {
 	long secs;
 
+#ifdef CONFIG_MMU
 	asm volatile("syscall"
 		: "=a" (secs)
 		: "0" (__NR_time), "D" (t) : "cc", "r11", "cx", "memory");
+#else
+	asm("call *%1"
+		: "=a" (secs)
+		: "0" ((unsigned long)__NR_time), "D" (t) : "cc", "r11", "cx", "memory");
+#endif
 
 	return secs;
 }
diff --git a/arch/x86/um/vdso/vma.c b/arch/x86/um/vdso/vma.c
index f238f7b33cdd..83c861e2a815 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>
 
 static unsigned int __read_mostly vdso_enabled = 1;
 unsigned long um_vdso_addr;
@@ -24,7 +25,9 @@ static int __init init_vdso(void)
 
 	BUG_ON(vdso_end - vdso_start > PAGE_SIZE);
 
+#ifdef CONFIG_MMU
 	um_vdso_addr = task_size - PAGE_SIZE;
+#endif
 
 	vdsop = kmalloc(sizeof(struct page *), GFP_KERNEL);
 	if (!vdsop)
@@ -40,6 +43,15 @@ static int __init init_vdso(void)
 	copy_page(page_address(um_vdso), vdso_start);
 	*vdsop = um_vdso;
 
+#ifndef CONFIG_MMU
+	/* 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, 1, 1);
+	pr_debug("vdso_start=%lx um_vdso_addr=%lx pg_um_vdso=%lx",
+	       (unsigned long)vdso_start, um_vdso_addr,
+	       (unsigned long)page_address(um_vdso));
+#endif
+
 	return 0;
 
 oom:
@@ -50,6 +62,7 @@ static int __init init_vdso(void)
 }
 subsys_initcall(init_vdso);
 
+#ifdef CONFIG_MMU
 int arch_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)
 {
 	struct vm_area_struct *vma;
@@ -74,3 +87,4 @@ int arch_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)
 
 	return IS_ERR(vma) ? PTR_ERR(vma) : 0;
 }
+#endif
-- 
2.43.0