linux-kernel - [PATCH 5.15 909/917] powerpc/security: Use a mutex for interrupt exit code patching

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: <20211115165459.863700428@linuxfoundation.org>
Date:   Mon, 15 Nov 2021 18:06:44 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Russell Currey <ruscur@...sell.cc>,
        Nicholas Piggin <npiggin@...il.com>,
        Michael Ellerman <mpe@...erman.id.au>
Subject: [PATCH 5.15 909/917] powerpc/security: Use a mutex for interrupt exit code patching

From: Russell Currey <ruscur@...sell.cc>

commit 3c12b4df8d5e026345a19886ae375b3ebc33c0b6 upstream.

The mitigation-patching.sh script in the powerpc selftests toggles
all mitigations on and off simultaneously, revealing that rfi_flush
and stf_barrier cannot safely operate at the same time due to races
in updating the static key.

On some systems, the static key code throws a warning and the kernel
remains functional.  On others, the kernel will hang or crash.

Fix this by slapping on a mutex.

Fixes: 13799748b957 ("powerpc/64: use interrupt restart table to speed up return from interrupt")
Cc: stable@...r.kernel.org # v5.14+
Signed-off-by: Russell Currey <ruscur@...sell.cc>
Acked-by: Nicholas Piggin <npiggin@...il.com>
Signed-off-by: Michael Ellerman <mpe@...erman.id.au>
Link: https://lore.kernel.org/r/20211027072410.40950-1-ruscur@russell.cc
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 arch/powerpc/lib/feature-fixups.c |   11 +++++++++++
 1 file changed, 11 insertions(+)

--- a/arch/powerpc/lib/feature-fixups.c
+++ b/arch/powerpc/lib/feature-fixups.c
@@ -228,6 +228,7 @@ static void do_stf_exit_barrier_fixups(e
 
 static bool stf_exit_reentrant = false;
 static bool rfi_exit_reentrant = false;
+static DEFINE_MUTEX(exit_flush_lock);
 
 static int __do_stf_barrier_fixups(void *data)
 {
@@ -253,6 +254,9 @@ void do_stf_barrier_fixups(enum stf_barr
 	 * low level interrupt exit code before patching. After the patching,
 	 * if allowed, then flip the branch to allow fast exits.
 	 */
+
+	// Prevent static key update races with do_rfi_flush_fixups()
+	mutex_lock(&exit_flush_lock);
 	static_branch_enable(&interrupt_exit_not_reentrant);
 
 	stop_machine(__do_stf_barrier_fixups, &types, NULL);
@@ -264,6 +268,8 @@ void do_stf_barrier_fixups(enum stf_barr
 
 	if (stf_exit_reentrant && rfi_exit_reentrant)
 		static_branch_disable(&interrupt_exit_not_reentrant);
+
+	mutex_unlock(&exit_flush_lock);
 }
 
 void do_uaccess_flush_fixups(enum l1d_flush_type types)
@@ -486,6 +492,9 @@ void do_rfi_flush_fixups(enum l1d_flush_
 	 * without stop_machine, so this could be achieved with a broadcast
 	 * IPI instead, but this matches the stf sequence.
 	 */
+
+	// Prevent static key update races with do_stf_barrier_fixups()
+	mutex_lock(&exit_flush_lock);
 	static_branch_enable(&interrupt_exit_not_reentrant);
 
 	stop_machine(__do_rfi_flush_fixups, &types, NULL);
@@ -497,6 +506,8 @@ void do_rfi_flush_fixups(enum l1d_flush_
 
 	if (stf_exit_reentrant && rfi_exit_reentrant)
 		static_branch_disable(&interrupt_exit_not_reentrant);
+
+	mutex_unlock(&exit_flush_lock);
 }
 
 void do_barrier_nospec_fixups_range(bool enable, void *fixup_start, void *fixup_end)