linux-kernel - [PATCH 16/16] x86_64, entry: Remove a bogus ret_from

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Thu, 26 Feb 2015 14:40:39 -0800
From:	Andy Lutomirski <luto@...capital.net>
To:	x86@...nel.org, linux-kernel@...r.kernel.org
Cc:	Borislav Petkov <bp@...en8.de>, Oleg Nesterov <oleg@...hat.com>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	Andy Lutomirski <luto@...capital.net>
Subject: [PATCH 16/16] x86_64, entry: Remove a bogus ret_from_fork optimization

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.

Acked-by: Ingo Molnar <mingo@...nel.org>
Signed-off-by: Andy Lutomirski <luto@...capital.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 4670fcdb5150..519498d1c8ec 100644
--- a/arch/x86/kernel/entry_64.S
+++ b/arch/x86/kernel/entry_64.S
@@ -550,11 +550,14 @@ ENTRY(ret_from_fork)
 	testl $3,CS(%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
-	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:
 	movq %rbp, %rdi
-- 
2.1.0

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/