[PATCH 3/6] x86/entry/vdso32: remove int80_landing_pad

["H. Peter Anvin" <hpa@zytor.com>]

There is no fundamental reason for the int80_landing_pad symbol. If ip
falls within the vdso, and the vdso is moved, we should change the ip
accordingly, regardless of mode or location within the vdso. This
*currently* can only happen on 32 bits, but there isn't any reason not
to do so generically.

Note that if this is ever possible from a vdso-internal call, then the
user space stack will also needed to be adjusted (as well as the
shadow stack, if enabled.) Fortunately this is not currently the case.

At the moment, we don't even consider other threads when moving the
vdso. The assumption is that it is only used by process freeze/thaw
for migration, where this is not an issue.

Signed-off-by: H. Peter Anvin (Intel) <hpa@zytor.com>
---
 arch/x86/entry/vdso/vdso32/system_call.S |  1 -
 arch/x86/entry/vdso/vma.c                | 16 ++++++----------
 arch/x86/tools/vdso2c.c                  |  1 -
 3 files changed, 6 insertions(+), 12 deletions(-)

diff --git a/arch/x86/entry/vdso/vdso32/system_call.S b/arch/x86/entry/vdso/vdso32/system_call.S
index 2a15634bbe75..d14eca4403c5 100644
--- a/arch/x86/entry/vdso/vdso32/system_call.S
+++ b/arch/x86/entry/vdso/vdso32/system_call.S
@@ -62,7 +62,6 @@ __kernel_vsyscall:
 
 	/* Enter using int $0x80 */
 	int	$0x80
-SYM_INNER_LABEL(int80_landing_pad, SYM_L_GLOBAL)
 
 	/*
 	 * Restore EDX and ECX in case they were clobbered.  EBP is not
diff --git a/arch/x86/entry/vdso/vma.c b/arch/x86/entry/vdso/vma.c
index 8f98c2d7c7a9..e7fd7517370f 100644
--- a/arch/x86/entry/vdso/vma.c
+++ b/arch/x86/entry/vdso/vma.c
@@ -65,16 +65,12 @@ static vm_fault_t vdso_fault(const struct vm_special_mapping *sm,
 static void vdso_fix_landing(const struct vdso_image *image,
 		struct vm_area_struct *new_vma)
 {
-	if (in_ia32_syscall() && image == &vdso32_image) {
-		struct pt_regs *regs = current_pt_regs();
-		unsigned long vdso_land = image->sym_int80_landing_pad;
-		unsigned long old_land_addr = vdso_land +
-			(unsigned long)current->mm->context.vdso;
-
-		/* Fixing userspace landing - look at do_fast_syscall_32 */
-		if (regs->ip == old_land_addr)
-			regs->ip = new_vma->vm_start + vdso_land;
-	}
+	struct pt_regs *regs = current_pt_regs();
+	unsigned long ipoffset = regs->ip -
+		(unsigned long)current->mm->context.vdso;
+
+	if (ipoffset < image->size)
+		regs->ip = new_vma->vm_start + ipoffset;
 }
 
 static int vdso_mremap(const struct vm_special_mapping *sm,
diff --git a/arch/x86/tools/vdso2c.c b/arch/x86/tools/vdso2c.c
index f84e8f8fa5fe..c81bb32b1e6c 100644
--- a/arch/x86/tools/vdso2c.c
+++ b/arch/x86/tools/vdso2c.c
@@ -79,7 +79,6 @@ struct vdso_sym required_syms[] = {
 	{"__kernel_vsyscall", true},
 	{"__kernel_sigreturn", true},
 	{"__kernel_rt_sigreturn", true},
-	{"int80_landing_pad", true},
 	{"vdso32_rt_sigreturn_landing_pad", true},
 	{"vdso32_sigreturn_landing_pad", true},
 };
-- 
2.51.1