[PATCH v2] arm64: Make kpti command line options x86 compatible

From: Alexander Graf
Date: Tue Nov 13 2018 - 10:29:14 EST


I've already stumbled over 2 cases where people got confused about how to
disable kpti on AArch64. In both cases, they used existing x86_64 options
and just applied that to an AArch64 system, expecting it to work.

I think it makes a lot of sense to have compatible kernel command line
parameters whenever we can have them be compatible.

So this patch adds the pti= and no_pti kernel command line options, mapping
them into the existing kpti= command line framework. It preserves the old
syntax to maintain compatibility with older command lines.

While at it, the patch also marks the respective options as dual-arch.

Reported-by: Richard Brown <rbrown@xxxxxxx>
Signed-off-by: Alexander Graf <agraf@xxxxxxx>

---

v1 -> v2:

- Actually make it compile. Sorry for the sloppy v1.
---
Documentation/admin-guide/kernel-parameters.txt | 6 +++---
arch/arm64/kernel/cpufeature.c | 20 +++++++++++++++++++-
2 files changed, 22 insertions(+), 4 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 81d1d5a74728..4a1c6bcfcdb5 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -3522,8 +3522,8 @@
pt. [PARIDE]
See Documentation/blockdev/paride.txt.

- pti= [X86_64] Control Page Table Isolation of user and
- kernel address spaces. Disabling this feature
+ pti= [X86_64,ARM64] Control Page Table Isolation of user
+ and kernel address spaces. Disabling this feature
removes hardening, but improves performance of
system calls and interrupts.

@@ -3534,7 +3534,7 @@

Not specifying this option is equivalent to pti=auto.

- nopti [X86_64]
+ nopti [X86_64,ARM64]
Equivalent to pti=off

pty.legacy_count=
diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index af50064dea51..a67b4b563a7c 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -978,13 +978,31 @@ static int __init parse_kpti(char *str)
bool enabled;
int ret = strtobool(str, &enabled);

- if (ret)
+ if (ret) {
+ if (!strncmp(str, "auto", 4)) {
+ __kpti_forced = 0;
+ return 0;
+ }
return ret;
+ }

__kpti_forced = enabled ? 1 : -1;
return 0;
}
early_param("kpti", parse_kpti);
+
+static int __init parse_pti(char *str)
+{
+ return parse_kpti(str);
+}
+early_param("pti", parse_pti);
+
+static int __init parse_no_pti(char *p)
+{
+ __kpti_forced = -1;
+ return 0;
+}
+early_param("nopti", parse_no_pti);
#endif /* CONFIG_UNMAP_KERNEL_AT_EL0 */

#ifdef CONFIG_ARM64_HW_AFDBM
--
2.12.3