UPSTREAM: arm64: kaslr: keep modules close to the kernel when DYNAMIC_FTRACE=y

The RANDOMIZE_MODULE_REGION_FULL Kconfig option allows KASLR to be
configured in such a way that kernel modules and the core kernel are
allocated completely independently, which implies that modules are likely
to require branches via PLT entries to reach the core kernel. The dynamic
ftrace code does not expect that, and assumes that it can patch module
code to perform a relative branch to anywhere in the core kernel. This
may result in errors such as

  branch_imm_common: offset out of range
  ------------[ cut here ]------------
  WARNING: CPU: 3 PID: 196 at kernel/trace/ftrace.c:1995 ftrace_bug+0x220/0x2e8
  Modules linked in:

  CPU: 3 PID: 196 Comm: systemd-udevd Not tainted 4.8.0-22-generic #24
  Hardware name: AMD Seattle/Seattle, BIOS 10:34:40 Oct  6 2016
  task: ffff8d1bef7dde80 task.stack: ffff8d1bef6b0000
  PC is at ftrace_bug+0x220/0x2e8
  LR is at ftrace_process_locs+0x330/0x430

So make RANDOMIZE_MODULE_REGION_FULL mutually exclusive with DYNAMIC_FTRACE
at the Kconfig level.

Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Bug: 30369029
(cherry picked from commit 8fe88a4145cdeee486af60e61f5d5a14f804fa45)
Signed-off-by: Jeff Vander Stoep <jeffv@google.com>
Change-Id: Ifb2474dcbb7a3066fe5724ee53a2048d61e80ccc

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 7f16989f8cb8dc463617aa513cf4f1c87cb13f9a..f4637c624db21170c79536d94e035c75b0e4e00d 100644 (file)
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -834,7 +834,7 @@ config RANDOMIZE_BASE
 
 config RANDOMIZE_MODULE_REGION_FULL
        bool "Randomize the module region independently from the core kernel"
-       depends on RANDOMIZE_BASE
+       depends on RANDOMIZE_BASE && !DYNAMIC_FTRACE
        default y
        help
          Randomizes the location of the module region without considering the