[PATCH] x86 tls prevent_tail_call

[Roland McGrath]

The x86 TLS cleanup in commit efd1ca52d04d2f6df337a3332cee56cd60e6d4c4
made the sys_set_thread_area and sys_get_thread_area functions ripe for
tail call optimization.  If the compiler chooses to use it for them, it
can clobber the user trap frame because these are asmlinkage functions.

Signed-off-by: Roland McGrath <roland@xxxxxxxxxx>
---
 arch/x86/kernel/tls.c |    8 ++++++--
 1 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/tls.c b/arch/x86/kernel/tls.c
index 6dfd4e7..022bcaa 100644
--- a/arch/x86/kernel/tls.c
+++ b/arch/x86/kernel/tls.c
@@ -91,7 +91,9 @@ int do_set_thread_area(struct task_struct *p, int idx,
 
 asmlinkage int sys_set_thread_area(struct user_desc __user *u_info)
 {
-	return do_set_thread_area(current, -1, u_info, 1);
+	int ret = do_set_thread_area(current, -1, u_info, 1);
+	prevent_tail_call(ret);
+	return ret;
 }
 
 
@@ -139,7 +141,9 @@ int do_get_thread_area(struct task_struct *p, int idx,
 
 asmlinkage int sys_get_thread_area(struct user_desc __user *u_info)
 {
-	return do_get_thread_area(current, -1, u_info);
+	int ret = do_get_thread_area(current, -1, u_info);
+	prevent_tail_call(ret);
+	return ret;
 }
 
 int regset_tls_active(struct task_struct *target,
--
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