[RFC/INCOMPLETE 07/13] x86/entry/64: Really create an error-entry-from-usermode code path

[Andy Lutomirski]

In 539f51136500 ("x86/asm/entry/64: Disentangle error_entry/exit
gsbase/ebx/usermode code"), I arranged the code slightly wrong --
IRET faults would skip the code path that was intended to execute on
all error entries from user mode.  Fix it up.

This does not fix a bug, but we'll need it, and it slightly shrinks
the code.

Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxx>
---
 arch/x86/entry/entry_64.S | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index 3bb2c4302df1..33acc3dcc281 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -1145,7 +1145,11 @@ ENTRY(error_entry)
 	testb	$3, CS+8(%rsp)
 	jz	error_kernelspace
 
-	/* We entered from user mode */
+error_entry_from_usermode:
+	/*
+	 * We entered from user mode or we're pretending to have entered
+	 * from user mode due to an IRET fault.
+	 */
 	SWAPGS
 
 error_entry_done:
@@ -1174,8 +1178,7 @@ error_kernelspace:
 	 * gsbase and proceed.  We'll fix up the exception and land in
 	 * gs_change's error handler with kernel gsbase.
 	 */
-	SWAPGS
-	jmp	error_entry_done
+	jmp	error_entry_from_usermode
 
 bstep_iret:
 	/* Fix truncated RIP */
-- 
2.4.3

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