[tip: x86/urgent] x86/ptrace: Remove set_segment_reg() implementations for current

[tip-bot2 for Andy Lutomirski]

The following commit has been merged into the x86/urgent branch of tip:

Commit-ID:     8e05f1b4f27d07a0f93e7c6fd28525a5d082b85c
Gitweb:        https://git.kernel.org/tip/8e05f1b4f27d07a0f93e7c6fd28525a5d082b85c
Author:        Andy Lutomirski <luto@xxxxxxxxxx>
AuthorDate:    Mon, 15 Jul 2019 10:08:48 -07:00
Committer:     Ingo Molnar <mingo@xxxxxxxxxx>
CommitterDate: Tue, 26 Nov 2019 22:00:12 +01:00

x86/ptrace: Remove set_segment_reg() implementations for current

seg_segment_reg() should be unreachable with task == current.
Rather than confusingly trying to make it work, just explicitly
disable this case.

(regset->get is used for current in the coredump code, but the ->set
 interface is only used for ptrace, and you can't ptrace yourself.)

Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
 arch/x86/kernel/ptrace.c | 19 +++++++------------
 1 file changed, 7 insertions(+), 12 deletions(-)

diff --git a/arch/x86/kernel/ptrace.c b/arch/x86/kernel/ptrace.c
index 066e5b0..3b3b169 100644
--- a/arch/x86/kernel/ptrace.c
+++ b/arch/x86/kernel/ptrace.c
@@ -182,6 +182,9 @@ static u16 get_segment_reg(struct task_struct *task, unsigned long offset)
 static int set_segment_reg(struct task_struct *task,
 			   unsigned long offset, u16 value)
 {
+	if (WARN_ON_ONCE(task == current))
+		return -EIO;
+
 	/*
 	 * The value argument was already truncated to 16 bits.
 	 */
@@ -209,10 +212,7 @@ static int set_segment_reg(struct task_struct *task,
 		break;
 
 	case offsetof(struct user_regs_struct, gs):
-		if (task == current)
-			set_user_gs(task_pt_regs(task), value);
-		else
-			task_user_gs(task) = value;
+		task_user_gs(task) = value;
 	}
 
 	return 0;
@@ -272,6 +272,9 @@ static u16 get_segment_reg(struct task_struct *task, unsigned long offset)
 static int set_segment_reg(struct task_struct *task,
 			   unsigned long offset, u16 value)
 {
+	if (WARN_ON_ONCE(task == current))
+		return -EIO;
+
 	/*
 	 * The value argument was already truncated to 16 bits.
 	 */
@@ -281,23 +284,15 @@ static int set_segment_reg(struct task_struct *task,
 	switch (offset) {
 	case offsetof(struct user_regs_struct,fs):
 		task->thread.fsindex = value;
-		if (task == current)
-			loadsegment(fs, task->thread.fsindex);
 		break;
 	case offsetof(struct user_regs_struct,gs):
 		task->thread.gsindex = value;
-		if (task == current)
-			load_gs_index(task->thread.gsindex);
 		break;
 	case offsetof(struct user_regs_struct,ds):
 		task->thread.ds = value;
-		if (task == current)
-			loadsegment(ds, task->thread.ds);
 		break;
 	case offsetof(struct user_regs_struct,es):
 		task->thread.es = value;
-		if (task == current)
-			loadsegment(es, task->thread.es);
 		break;
 
 		/*