| From foo@baz Wed Aug 22 09:42:09 CEST 2018 |
| From: "Steven Rostedt (VMware)" <rostedt@goodmis.org> |
| Date: Tue, 10 Jul 2018 08:22:40 +0100 |
| Subject: ARM: 8780/1: ftrace: Only set kernel memory back to read-only after boot |
| |
| From: "Steven Rostedt (VMware)" <rostedt@goodmis.org> |
| |
| [ Upstream commit b4c7e2bd2eb4764afe3af9409ff3b1b87116fa30 ] |
| |
| Dynamic ftrace requires modifying the code segments that are usually |
| set to read-only. To do this, a per arch function is called both before |
| and after the ftrace modifications are performed. The "before" function |
| will set kernel code text to read-write to allow for ftrace to make the |
| modifications, and the "after" function will set the kernel code text |
| back to "read-only" to keep the kernel code text protected. |
| |
| The issue happens when dynamic ftrace is tested at boot up. The test is |
| done before the kernel code text has been set to read-only. But the |
| "before" and "after" calls are still performed. The "after" call will |
| change the kernel code text to read-only prematurely, and other boot |
| code that expects this code to be read-write will fail. |
| |
| The solution is to add a variable that is set when the kernel code text |
| is expected to be converted to read-only, and make the ftrace "before" |
| and "after" calls do nothing if that variable is not yet set. This is |
| similar to the x86 solution from commit 162396309745 ("ftrace, x86: |
| make kernel text writable only for conversions"). |
| |
| Link: http://lkml.kernel.org/r/20180620212906.24b7b66e@vmware.local.home |
| |
| Reported-by: Stefan Agner <stefan@agner.ch> |
| Tested-by: Stefan Agner <stefan@agner.ch> |
| Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org> |
| Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk> |
| Signed-off-by: Sasha Levin <alexander.levin@microsoft.com> |
| Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| --- |
| arch/arm/mm/init.c | 9 +++++++++ |
| 1 file changed, 9 insertions(+) |
| |
| --- a/arch/arm/mm/init.c |
| +++ b/arch/arm/mm/init.c |
| @@ -722,19 +722,28 @@ int __mark_rodata_ro(void *unused) |
| return 0; |
| } |
| |
| +static int kernel_set_to_readonly __read_mostly; |
| + |
| void mark_rodata_ro(void) |
| { |
| + kernel_set_to_readonly = 1; |
| stop_machine(__mark_rodata_ro, NULL, NULL); |
| } |
| |
| void set_kernel_text_rw(void) |
| { |
| + if (!kernel_set_to_readonly) |
| + return; |
| + |
| set_section_perms(ro_perms, ARRAY_SIZE(ro_perms), false, |
| current->active_mm); |
| } |
| |
| void set_kernel_text_ro(void) |
| { |
| + if (!kernel_set_to_readonly) |
| + return; |
| + |
| set_section_perms(ro_perms, ARRAY_SIZE(ro_perms), true, |
| current->active_mm); |
| } |