ret_from_fork checks TIF_IA32 to determine whether pt_regs and the
related state make sense for ret_from_sys_call. This is entirely
the wrong check. TS_COMPAT would make a little more sense, but
there's really no point in keeping this optimization at all.
This fixes a return to the wrong user CS if we came from int 0x80 in
a 64-bit task.
Signed-off-by: Andy Lutomirski <l...@amacapital.net>
---
arch/x86/kernel/entry_64.S | 13 ++++++++-----
1 file changed, 8 insertions(+), 5 deletions(-)
diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
index 9ebaf63ba182..4ee9a2315f80 100644
--- a/arch/x86/kernel/entry_64.S
+++ b/arch/x86/kernel/entry_64.S
@@ -334,11 +334,14 @@ ENTRY(ret_from_fork)
testl $3, CS-ARGOFFSET(%rsp) # from kernel_thread?
jz 1f
- testl $_TIF_IA32, TI_flags(%rcx) # 32-bit compat task needs IRET
- jnz int_ret_from_sys_call
-
- RESTORE_TOP_OF_STACK %rdi, -ARGOFFSET
- jmp ret_from_sys_call # go to the SYSRET fastpath
+ /*
+ * By the time we get here, we have no idea whether our pt_regs,
+ * ti flags, and ti status came from the 64-bit SYSCALL fast path,
+ * the slow path, or one of the ia32entry paths.
+ * Use int_ret_from_sys_call to return, since it can safely handle
+ * all of the above.
+ */
+ jmp int_ret_from_sys_call
1:
subq $REST_SKIP, %rsp # leave space for volatiles
--
2.3.0
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