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84 lines
3 KiB
Diff
84 lines
3 KiB
Diff
From 786b6ff17f8612ba9af84ac379d4b494f39f55c5 Mon Sep 17 00:00:00 2001
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From: Steven Rostedt <rostedt@goodmis.org>
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Date: Wed, 23 Aug 2017 13:58:36 -0400
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Subject: [PATCH 374/374] Arm: mm: ftrace: Only set text back to ro after
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kernel has been marked ro
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ftrace needs to modify the kernel text in order to enable function tracing.
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For security reasons, the kernel text is marked to read-only (ro) at the end
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of system bootup. When enabling function tracing after that, ftrace calls
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arch specific code that needs to enable the modification of kernel text
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while ftrace does the update, and reset it back again when finished.
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The issue arises when function tracing is enabled during system bootup. The
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text hasn't been marked as read-only yet, but the same code to modify the
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kernel is executed, and when it is finished, it will cause the kernel to
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become read-only. This causes issues for other init code that requires
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modification of kernel text during system bootup. This appears to cause
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issue with Raspberry Pi 2.
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By implementing the feature that is used in x86 to deal with this issue, it
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fixes the problem. The solution is simple. Have a variable
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(kernel_set_to_readonly) get set when the system finished boot and marks the
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kernel to readonly. If that variable is not set, both
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kernel_set_to_readonly() and kernel_set_to_rw() return without doing any
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modifications. Those functions are used by ftrace to change the permissions
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of the kernel text. By not doing anything, ftrace will not mess with the
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permissions when it is enabled at system bootup.
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Link: http://lkml.kernel.org/r/20170821153402.7so2u364htvt6tnf@camel2.lan
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Link: https://github.com/raspberrypi/linux/issues/2166#issuecomment-323355145
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Reported-by: Matthias Reichl <hias@horus.com>
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Cc: Russell King <linux@armlinux.org.uk>
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Cc: Kees Cook <keescook@chromium.org>
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Cc: Eric Anholt <eric@anholt.net>
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Cc: Stefan Wahren <stefan.wahren@i2se.com>
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Cc: Phil Elwell <phil@raspberrypi.org>
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Cc: linux-rpi-kernel@lists.infradead.org
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Cc: linux-arm-kernel@lists.infradead.org
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Cc: stable@vger.kernel.org
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Fixes: 80d6b0c2ee ("ARM: mm: allow text and rodata sections to be read-only")
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Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
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Tested-by: Matthias Reichl <hias@horus.com>
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Acked-by: Kees Cook <keescook@chromium.org>
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---
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arch/arm/mm/init.c | 10 ++++++++++
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1 file changed, 10 insertions(+)
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diff --git a/arch/arm/mm/init.c b/arch/arm/mm/init.c
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index 0f6d1537f330..82175c047222 100644
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--- a/arch/arm/mm/init.c
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+++ b/arch/arm/mm/init.c
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@@ -745,19 +745,29 @@ static int __mark_rodata_ro(void *unused)
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return 0;
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}
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+static int kernel_set_to_readonly;
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+
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void mark_rodata_ro(void)
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{
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+ kernel_set_to_readonly = 1;
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+
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stop_machine(__mark_rodata_ro, NULL, NULL);
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}
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void set_kernel_text_rw(void)
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{
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+ if (!kernel_set_to_readonly)
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+ return;
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+
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set_section_perms(ro_perms, ARRAY_SIZE(ro_perms), false,
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current->active_mm);
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}
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void set_kernel_text_ro(void)
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{
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+ if (!kernel_set_to_readonly)
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+ return;
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+
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set_section_perms(ro_perms, ARRAY_SIZE(ro_perms), true,
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current->active_mm);
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}
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--
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2.16.1
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