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authorDaniel Axtens <dja@axtens.net>2022-05-18 13:05:31 +0300
committerMichael Ellerman <mpe@ellerman.id.au>2022-05-22 08:58:29 +0300
commit41b7a347bf1491e7300563bb224432608b41f62a (patch)
tree4160455f1424493f2508b297d6071e12b69c4b2b /arch/powerpc/platforms
parent2ab2d5794f14c08676690bf0859f16cc768bb3a4 (diff)
downloadlinux-41b7a347bf1491e7300563bb224432608b41f62a.tar.xz
powerpc: Book3S 64-bit outline-only KASAN support
Implement a limited form of KASAN for Book3S 64-bit machines running under the Radix MMU, supporting only outline mode. - Enable the compiler instrumentation to check addresses and maintain the shadow region. (This is the guts of KASAN which we can easily reuse.) - Require kasan-vmalloc support to handle modules and anything else in vmalloc space. - KASAN needs to be able to validate all pointer accesses, but we can't instrument all kernel addresses - only linear map and vmalloc. On boot, set up a single page of read-only shadow that marks all iomap and vmemmap accesses as valid. - Document KASAN in powerpc docs. Background ---------- KASAN support on Book3S is a bit tricky to get right: - It would be good to support inline instrumentation so as to be able to catch stack issues that cannot be caught with outline mode. - Inline instrumentation requires a fixed offset. - Book3S runs code with translations off ("real mode") during boot, including a lot of generic device-tree parsing code which is used to determine MMU features. [ppc64 mm note: The kernel installs a linear mapping at effective address c000...-c008.... This is a one-to-one mapping with physical memory from 0000... onward. Because of how memory accesses work on powerpc 64-bit Book3S, a kernel pointer in the linear map accesses the same memory both with translations on (accessing as an 'effective address'), and with translations off (accessing as a 'real address'). This works in both guests and the hypervisor. For more details, see s5.7 of Book III of version 3 of the ISA, in particular the Storage Control Overview, s5.7.3, and s5.7.5 - noting that this KASAN implementation currently only supports Radix.] - Some code - most notably a lot of KVM code - also runs with translations off after boot. - Therefore any offset has to point to memory that is valid with translations on or off. One approach is just to give up on inline instrumentation. This way boot-time checks can be delayed until after the MMU is set is up, and we can just not instrument any code that runs with translations off after booting. Take this approach for now and require outline instrumentation. Previous attempts allowed inline instrumentation. However, they came with some unfortunate restrictions: only physically contiguous memory could be used and it had to be specified at compile time. Maybe we can do better in the future. [paulus@ozlabs.org - Rebased onto 5.17. Note that a kernel with CONFIG_KASAN=y will crash during boot on a machine using HPT translation because not all the entry points to the generic KASAN code are protected with a call to kasan_arch_is_ready().] Originally-by: Balbir Singh <bsingharora@gmail.com> # ppc64 out-of-line radix version Signed-off-by: Daniel Axtens <dja@axtens.net> Signed-off-by: Paul Mackerras <paulus@ozlabs.org> [mpe: Update copyright year and comment formatting] Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://lore.kernel.org/r/YoTE69OQwiG7z+Gu@cleo
Diffstat (limited to 'arch/powerpc/platforms')
-rw-r--r--arch/powerpc/platforms/Kconfig.cputype1
-rw-r--r--arch/powerpc/platforms/powernv/Makefile8
-rw-r--r--arch/powerpc/platforms/pseries/Makefile2
3 files changed, 11 insertions, 0 deletions
diff --git a/arch/powerpc/platforms/Kconfig.cputype b/arch/powerpc/platforms/Kconfig.cputype
index 942606b2b193..9e2df4b66478 100644
--- a/arch/powerpc/platforms/Kconfig.cputype
+++ b/arch/powerpc/platforms/Kconfig.cputype
@@ -104,6 +104,7 @@ config PPC_BOOK3S_64
select HAVE_MOVE_PUD
select IRQ_WORK
select PPC_64S_HASH_MMU if !PPC_RADIX_MMU
+ select KASAN_VMALLOC if KASAN
config PPC_BOOK3E_64
bool "Embedded processors"
diff --git a/arch/powerpc/platforms/powernv/Makefile b/arch/powerpc/platforms/powernv/Makefile
index dc7b37c23b60..6488b3842199 100644
--- a/arch/powerpc/platforms/powernv/Makefile
+++ b/arch/powerpc/platforms/powernv/Makefile
@@ -1,4 +1,12 @@
# SPDX-License-Identifier: GPL-2.0
+
+# nothing that deals with real mode is safe to KASAN
+# in particular, idle code runs a bunch of things in real mode
+KASAN_SANITIZE_idle.o := n
+KASAN_SANITIZE_pci-ioda.o := n
+# pnv_machine_check_early
+KASAN_SANITIZE_setup.o := n
+
obj-y += setup.o opal-call.o opal-wrappers.o opal.o opal-async.o
obj-y += idle.o opal-rtc.o opal-nvram.o opal-lpc.o opal-flash.o
obj-y += rng.o opal-elog.o opal-dump.o opal-sysparam.o opal-sensor.o
diff --git a/arch/powerpc/platforms/pseries/Makefile b/arch/powerpc/platforms/pseries/Makefile
index a1fab0955bf4..7aaff5323544 100644
--- a/arch/powerpc/platforms/pseries/Makefile
+++ b/arch/powerpc/platforms/pseries/Makefile
@@ -34,4 +34,6 @@ obj-$(CONFIG_PPC_VAS) += vas.o vas-sysfs.o
obj-$(CONFIG_ARCH_HAS_CC_PLATFORM) += cc_platform.o
+# nothing that operates in real mode is safe for KASAN
+KASAN_SANITIZE_ras.o := n
KASAN_SANITIZE_kexec.o := n