[PATCH -tip v2 1/2] x86/ptrace: Use savesegment() in get_segment_reg() instead of inline asm

[PATCH -tip v2 1/2] x86/ptrace: Use savesegment() in get_segment_reg() instead of inline asm

[Uros Bizjak]

Replace direct 'movl' instructions for DS, ES, FS, and GS read in
get_segment_reg() with the savesegment() helper. This improves
readability, consistency, and ensures proper handling of
segment registers on x86_64.

No functional change intended.

Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Acked-by: Oleg Nesterov <oleg@redhat.com>
Cc: Thomas Gleixner <tglx@kernel.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
---
 arch/x86/kernel/ptrace.c | 19 +++++++++----------
 1 file changed, 9 insertions(+), 10 deletions(-)

diff --git a/arch/x86/kernel/ptrace.c b/arch/x86/kernel/ptrace.c
index 3dcadc13f09a..4cb00aa0645f 100644
--- a/arch/x86/kernel/ptrace.c
+++ b/arch/x86/kernel/ptrace.c
@@ -251,32 +251,31 @@ static u16 get_segment_reg(struct task_struct *task, unsigned long offset)
 	/*
 	 * Returning the value truncates it to 16 bits.
 	 */
-	unsigned int seg;
+	unsigned int retval;
 
 	switch (offset) {
 	case offsetof(struct user_regs_struct, fs):
 		if (task == current) {
-			/* Older gas can't assemble movq %?s,%r?? */
-			asm("movl %%fs,%0" : "=r" (seg));
-			return seg;
+			savesegment(fs, retval);
+			return retval;
 		}
 		return task->thread.fsindex;
 	case offsetof(struct user_regs_struct, gs):
 		if (task == current) {
-			asm("movl %%gs,%0" : "=r" (seg));
-			return seg;
+			savesegment(gs, retval);
+			return retval;
 		}
 		return task->thread.gsindex;
 	case offsetof(struct user_regs_struct, ds):
 		if (task == current) {
-			asm("movl %%ds,%0" : "=r" (seg));
-			return seg;
+			savesegment(ds, retval);
+			return retval;
 		}
 		return task->thread.ds;
 	case offsetof(struct user_regs_struct, es):
 		if (task == current) {
-			asm("movl %%es,%0" : "=r" (seg));
-			return seg;
+			savesegment(es, retval);
+			return retval;
 		}
 		return task->thread.es;
 
-- 
2.53.0

[PATCH -tip v2 2/2] x86/ptrace: Use unsigned short for segment values in get_segment_reg()

[Uros Bizjak]

Change the temporary variable in get_segment_reg() from unsigned int
to unsigned short to match the function’s return type, making the
16-bit semantics explicit instead of relying on implicit truncation.

Also restructure the GS handling for x86_32 to make the special case
explicit and easier to follow.

This clarifies the control flow and makes the 16-bit semantics
explicit without changing behavior.

No functional change intended.

Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Acked-by: Oleg Nesterov <oleg@redhat.com>
Cc: Thomas Gleixner <tglx@kernel.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
---
v2: New patch.
---
 arch/x86/kernel/ptrace.c | 24 +++++++++---------------
 1 file changed, 9 insertions(+), 15 deletions(-)

diff --git a/arch/x86/kernel/ptrace.c b/arch/x86/kernel/ptrace.c
index 4cb00aa0645f..58e09a764bcf 100644
--- a/arch/x86/kernel/ptrace.c
+++ b/arch/x86/kernel/ptrace.c
@@ -182,19 +182,16 @@ static unsigned long *pt_regs_access(struct pt_regs *regs, unsigned long regno)
 
 static u16 get_segment_reg(struct task_struct *task, unsigned long offset)
 {
-	/*
-	 * Returning the value truncates it to 16 bits.
-	 */
-	unsigned int retval;
-	if (offset != offsetof(struct user_regs_struct, gs))
-		retval = *pt_regs_access(task_pt_regs(task), offset);
-	else {
-		if (task == current)
+	unsigned short retval;
+
+	if (offset == offsetof(struct user_regs_struct, gs)) {
+		if (task == current) {
 			savesegment(gs, retval);
-		else
-			retval = task->thread.gs;
+			return retval;
+		}
+		return task->thread.gs;
 	}
-	return retval;
+	return *pt_regs_access(task_pt_regs(task), offset);
 }
 
 static int set_segment_reg(struct task_struct *task,
@@ -248,10 +245,7 @@ static unsigned long *pt_regs_access(struct pt_regs *regs, unsigned long offset)
 
 static u16 get_segment_reg(struct task_struct *task, unsigned long offset)
 {
-	/*
-	 * Returning the value truncates it to 16 bits.
-	 */
-	unsigned int retval;
+	unsigned short retval;
 
 	switch (offset) {
 	case offsetof(struct user_regs_struct, fs):
-- 
2.53.0