linux-kernel - [patch 3/3] x86/cpu: Re-enable stackprotector

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]

Message-ID: <20220718173924.009884744@linutronix.de>
Date:   Mon, 18 Jul 2022 19:52:12 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     LKML <linux-kernel@...r.kernel.org>
Cc:     x86@...nel.org, Linus Torvalds <torvalds@...ux-foundation.org>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Josh Poimboeuf <jpoimboe@...nel.org>,
        Andrew Cooper <Andrew.Cooper3@...rix.com>,
        Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
        Johannes Wikner <kwikner@...z.ch>,
        Alyssa Milburn <alyssa.milburn@...ux.intel.com>,
        Jann Horn <jannh@...gle.com>, "H.J. Lu" <hjl.tools@...il.com>,
        Joao Moreira <joao.moreira@...el.com>,
        Joseph Nuzman <joseph.nuzman@...el.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Juergen Gross <jgross@...e.com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>
Subject: [patch 3/3] x86/cpu: Re-enable stackprotector

Commit 5416c2663517 ("x86: make sure load_percpu_segment has no
stackprotector") disabled the stackprotector for cpu/common.c because of
load_percpu_segment(). Back then the boot stack canary was initialized very
early in start_kernel(). Switching the per CPU area by loading the GDT
caused the stackprotector to fail with paravirt enabled kernels as the
GSBASE was not updated yet. In hindsight a wrong change because it would
have been sufficient to ensure that the canary is the same in both per CPU
areas.

Commit d55535232c3d ("random: move rand_initialize() earlier") moved the
stack canary initialization to a later point in the init sequence. As a
consequence the per CPU stack canary is 0 when switching the per CPU areas,
so there is no requirement anymore to exclude this file.

Add a comment to load_percpu_segment().

Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
---
 arch/x86/kernel/cpu/Makefile |    3 ---
 arch/x86/kernel/cpu/common.c |    3 +++
 2 files changed, 3 insertions(+), 3 deletions(-)

--- a/arch/x86/kernel/cpu/Makefile
+++ b/arch/x86/kernel/cpu/Makefile
@@ -16,9 +16,6 @@ KCOV_INSTRUMENT_perf_event.o := n
 # As above, instrumenting secondary CPU boot code causes boot hangs.
 KCSAN_SANITIZE_common.o := n
 
-# Make sure load_percpu_segment has no stackprotector
-CFLAGS_common.o		:= -fno-stack-protector
-
 obj-y			:= cacheinfo.o scattered.o topology.o
 obj-y			+= common.o
 obj-y			+= rdrand.o
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -751,6 +751,9 @@ void __init switch_to_direct_gdt(int cpu
 	 * wrmsrl() happens the early mapping is still valid. That means
 	 * the GSBASE update will lose any prior per CPU data which was
 	 * not copied over in setup_per_cpu_areas().
+	 *
+	 * This works even with stackprotector enabled because the
+	 * per CPU stack canary is 0 in both per CPU areas.
 	 */
 	if (IS_ENABLED(CONFIG_X86_64))
 		wrmsrl(MSR_GS_BASE, cpu_kernelmode_gs_base(cpu));