This is a note to let you know that I've just added the patch titled
arm64: entry: Add fake CPU feature for unmapping the kernel at EL0
to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
arm64-entry-add-fake-cpu-feature-for-unmapping-the-kernel-at-el0.patch
and it can be found in the queue-4.9 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From foo@baz Thu Apr 5 21:39:28 CEST 2018
From: Mark Rutland <mark.rutland@xxxxxxx>
Date: Tue, 3 Apr 2018 12:09:09 +0100
Subject: arm64: entry: Add fake CPU feature for unmapping the kernel at EL0
To: stable@xxxxxxxxxxxxxxx
Cc: mark.brown@xxxxxxxxxx, ard.biesheuvel@xxxxxxxxxx, marc.zyngier@xxxxxxx, will.deacon@xxxxxxx
Message-ID: <20180403110923.43575-14-mark.rutland@xxxxxxx>
From: Will Deacon <will.deacon@xxxxxxx>
commit ea1e3de85e94 upstream.
Allow explicit disabling of the entry trampoline on the kernel command
line (kpti=off) by adding a fake CPU feature (ARM64_UNMAP_KERNEL_AT_EL0)
that can be used to toggle the alternative sequences in our entry code and
avoid use of the trampoline altogether if desired. This also allows us to
make use of a static key in arm64_kernel_unmapped_at_el0().
Reviewed-by: Mark Rutland <mark.rutland@xxxxxxx>
Tested-by: Laura Abbott <labbott@xxxxxxxxxx>
Tested-by: Shanker Donthineni <shankerd@xxxxxxxxxxxxxx>
Signed-off-by: Will Deacon <will.deacon@xxxxxxx>
[Alex: use first free cpucap number, use cpus_have_cap]
Signed-off-by: Alex Shi <alex.shi@xxxxxxxxxx> [v4.9 backport]
Signed-off-by: Mark Rutland <mark.rutland@xxxxxxx> [v4.9 backport]
Tested-by: Will Deacon <will.deacon@xxxxxxx>
Tested-by: Greg Hackmann <ghackmann@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/arm64/include/asm/cpucaps.h | 3 +-
arch/arm64/include/asm/mmu.h | 3 +-
arch/arm64/kernel/cpufeature.c | 41 +++++++++++++++++++++++++++++++++++++++
arch/arm64/kernel/entry.S | 9 ++++----
4 files changed, 50 insertions(+), 6 deletions(-)
--- a/arch/arm64/include/asm/cpucaps.h
+++ b/arch/arm64/include/asm/cpucaps.h
@@ -34,7 +34,8 @@
#define ARM64_HAS_32BIT_EL0 13
#define ARM64_HYP_OFFSET_LOW 14
#define ARM64_MISMATCHED_CACHE_LINE_SIZE 15
+#define ARM64_UNMAP_KERNEL_AT_EL0 16
-#define ARM64_NCAPS 16
+#define ARM64_NCAPS 17
#endif /* __ASM_CPUCAPS_H */
--- a/arch/arm64/include/asm/mmu.h
+++ b/arch/arm64/include/asm/mmu.h
@@ -34,7 +34,8 @@ typedef struct {
static inline bool arm64_kernel_unmapped_at_el0(void)
{
- return IS_ENABLED(CONFIG_UNMAP_KERNEL_AT_EL0);
+ return IS_ENABLED(CONFIG_UNMAP_KERNEL_AT_EL0) &&
+ cpus_have_cap(ARM64_UNMAP_KERNEL_AT_EL0);
}
extern void paging_init(void);
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -746,6 +746,40 @@ static bool hyp_offset_low(const struct
return idmap_addr > GENMASK(VA_BITS - 2, 0) && !is_kernel_in_hyp_mode();
}
+#ifdef CONFIG_UNMAP_KERNEL_AT_EL0
+static int __kpti_forced; /* 0: not forced, >0: forced on, <0: forced off */
+
+static bool unmap_kernel_at_el0(const struct arm64_cpu_capabilities *entry,
+ int __unused)
+{
+ /* Forced on command line? */
+ if (__kpti_forced) {
+ pr_info_once("kernel page table isolation forced %s by command line option\n",
+ __kpti_forced > 0 ? "ON" : "OFF");
+ return __kpti_forced > 0;
+ }
+
+ /* Useful for KASLR robustness */
+ if (IS_ENABLED(CONFIG_RANDOMIZE_BASE))
+ return true;
+
+ return false;
+}
+
+static int __init parse_kpti(char *str)
+{
+ bool enabled;
+ int ret = strtobool(str, &enabled);
+
+ if (ret)
+ return ret;
+
+ __kpti_forced = enabled ? 1 : -1;
+ return 0;
+}
+__setup("kpti=", parse_kpti);
+#endif /* CONFIG_UNMAP_KERNEL_AT_EL0 */
+
static const struct arm64_cpu_capabilities arm64_features[] = {
{
.desc = "GIC system register CPU interface",
@@ -829,6 +863,13 @@ static const struct arm64_cpu_capabiliti
.def_scope = SCOPE_SYSTEM,
.matches = hyp_offset_low,
},
+#ifdef CONFIG_UNMAP_KERNEL_AT_EL0
+ {
+ .capability = ARM64_UNMAP_KERNEL_AT_EL0,
+ .def_scope = SCOPE_SYSTEM,
+ .matches = unmap_kernel_at_el0,
+ },
+#endif
{},
};
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -73,6 +73,7 @@
.macro kernel_ventry, el, label, regsize = 64
.align 7
#ifdef CONFIG_UNMAP_KERNEL_AT_EL0
+alternative_if ARM64_UNMAP_KERNEL_AT_EL0
.if \el == 0
.if \regsize == 64
mrs x30, tpidrro_el0
@@ -81,6 +82,7 @@
mov x30, xzr
.endif
.endif
+alternative_else_nop_endif
#endif
sub sp, sp, #S_FRAME_SIZE
@@ -208,10 +210,9 @@ alternative_else_nop_endif
ldr lr, [sp, #S_LR]
add sp, sp, #S_FRAME_SIZE // restore sp
-#ifndef CONFIG_UNMAP_KERNEL_AT_EL0
- eret
-#else
.if \el == 0
+alternative_insn eret, nop, ARM64_UNMAP_KERNEL_AT_EL0
+#ifdef CONFIG_UNMAP_KERNEL_AT_EL0
bne 4f
msr far_el1, x30
tramp_alias x30, tramp_exit_native
@@ -219,10 +220,10 @@ alternative_else_nop_endif
4:
tramp_alias x30, tramp_exit_compat
br x30
+#endif
.else
eret
.endif
-#endif
.endm
.macro get_thread_info, rd
Patches currently in stable-queue which might be from mark.rutland@xxxxxxx are
queue-4.9/arm64-mm-add-arm64_kernel_unmapped_at_el0-helper.patch
queue-4.9/arm64-entry-reword-comment-about-post_ttbr_update_workaround.patch
queue-4.9/arm64-kaslr-put-kernel-vectors-address-in-separate-data-page.patch
queue-4.9/arm64-turn-on-kpti-only-on-cpus-that-need-it.patch
queue-4.9/arm64-force-kpti-to-be-disabled-on-cavium-thunderx.patch
queue-4.9/arm64-mm-allocate-asids-in-pairs.patch
queue-4.9/arm64-tls-avoid-unconditional-zeroing-of-tpidrro_el0-for-native-tasks.patch
queue-4.9/arm64-use-ret-instruction-for-exiting-the-trampoline.patch
queue-4.9/arm64-entry-explicitly-pass-exception-level-to-kernel_ventry-macro.patch
queue-4.9/arm64-kpti-make-use-of-ng-dependent-on-arm64_kernel_unmapped_at_el0.patch
queue-4.9/arm64-mm-use-non-global-mappings-for-kernel-space.patch
queue-4.9/arm64-capabilities-handle-duplicate-entries-for-a-capability.patch
queue-4.9/arm64-entry-hook-up-entry-trampoline-to-exception-vectors.patch
queue-4.9/arm64-mm-invalidate-both-kernel-and-user-asids-when-performing-tlbi.patch
queue-4.9/arm64-mm-map-entry-trampoline-into-trampoline-and-kernel-page-tables.patch
queue-4.9/module-extend-rodata-off-boot-cmdline-parameter-to-module-mappings.patch
queue-4.9/arm64-kconfig-reword-unmap_kernel_at_el0-kconfig-entry.patch
queue-4.9/arm64-mm-move-asid-from-ttbr0-to-ttbr1.patch
queue-4.9/arm64-allow-checking-of-a-cpu-local-erratum.patch
queue-4.9/arm64-take-into-account-id_aa64pfr0_el1.csv3.patch
queue-4.9/arm64-kconfig-add-config_unmap_kernel_at_el0.patch
queue-4.9/arm64-idmap-use-awx-flags-for-.idmap.text-.pushsection-directives.patch
queue-4.9/arm64-factor-out-entry-stack-manipulation.patch
queue-4.9/arm64-entry-add-exception-trampoline-page-for-exceptions-from-el0.patch
queue-4.9/arm64-kpti-add-enable-callback-to-remap-swapper-using-ng-mappings.patch
queue-4.9/arm64-entry-add-fake-cpu-feature-for-unmapping-the-kernel-at-el0.patch
queue-4.9/arm64-cputype-add-midr-values-for-cavium-thunderx2-cpus.patch