Christophe Leroy <christophe.leroy@xxxxxx> writes: > Le 19/12/2019 à 10:50, Daniel Axtens a écrit : >> Christophe Leroy <christophe.leroy@xxxxxx> writes: >> >>> On 12/19/2019 12:36 AM, Daniel Axtens wrote: >>>> 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 in real mode after booting. Most notably a lot of KVM >>>> runs in real mode, and it would be good to be able to instrument it. >>>> >>>> - Because code runs in real mode after boot, the offset has to point to >>>> valid memory both in and out of real mode. >>>> >>>> [ppc64 mm note: The kernel installs a linear mapping at effective >>>> address c000... onward. 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.] >>>> >>>> One approach is just to give up on inline instrumentation. This way all >>>> checks can be delayed until after everything set is up correctly, and the >>>> address-to-shadow calculations can be overridden. However, the features and >>>> speed boost provided by inline instrumentation are worth trying to do >>>> better. >>>> >>>> If _at compile time_ it is known how much contiguous physical memory a >>>> system has, the top 1/8th of the first block of physical memory can be set >>>> aside for the shadow. This is a big hammer and comes with 3 big >>>> consequences: >>>> >>>> - there's no nice way to handle physically discontiguous memory, so only >>>> the first physical memory block can be used. >>>> >>>> - kernels will simply fail to boot on machines with less memory than >>>> specified when compiling. >>>> >>>> - kernels running on machines with more memory than specified when >>>> compiling will simply ignore the extra memory. >>>> >>>> Implement and document KASAN this way. The current implementation is Radix >>>> only. >>>> >>>> Despite the limitations, it can still find bugs, >>>> e.g. http://patchwork.ozlabs.org/patch/1103775/ >>>> >>>> At the moment, this physical memory limit must be set _even for outline >>>> mode_. This may be changed in a later series - a different implementation >>>> could be added for outline mode that dynamically allocates shadow at a >>>> fixed offset. For example, see https://patchwork.ozlabs.org/patch/795211/ >>>> >>>> Suggested-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx> >>>> Cc: Balbir Singh <bsingharora@xxxxxxxxx> # ppc64 out-of-line radix version >>>> Cc: Christophe Leroy <christophe.leroy@xxxxxx> # ppc32 version >>>> Signed-off-by: Daniel Axtens <dja@xxxxxxxxxx> >>>> >>>> --- >>>> Changes since v3: >>>> - Address further feedback from Christophe. >>>> - Drop changes to stack walking, it looks like the issue I observed is >>>> related to that particular stack, not stack-walking generally. >>>> >>>> Changes since v2: >>>> >>>> - Address feedback from Christophe around cleanups and docs. >>>> - Address feedback from Balbir: at this point I don't have a good solution >>>> for the issues you identify around the limitations of the inline implementation >>>> but I think that it's worth trying to get the stack instrumentation support. >>>> I'm happy to have an alternative and more flexible outline mode - I had >>>> envisoned this would be called 'lightweight' mode as it imposes fewer restrictions. >>>> I've linked to your implementation. I think it's best to add it in a follow-up series. >>>> - Made the default PHYS_MEM_SIZE_FOR_KASAN value 1024MB. I think most people have >>>> guests with at least that much memory in the Radix 64s case so it's a much >>>> saner default - it means that if you just turn on KASAN without reading the >>>> docs you're much more likely to have a bootable kernel, which you will never >>>> have if the value is set to zero! I'm happy to bikeshed the value if we want. >>>> >>>> Changes since v1: >>>> - Landed kasan vmalloc support upstream >>>> - Lots of feedback from Christophe. >>>> >>>> Changes since the rfc: >>>> >>>> - Boots real and virtual hardware, kvm works. >>>> >>>> - disabled reporting when we're checking the stack for exception >>>> frames. The behaviour isn't wrong, just incompatible with KASAN. >>>> >>>> - Documentation! >>>> >>>> - Dropped old module stuff in favour of KASAN_VMALLOC. >>>> >>>> The bugs with ftrace and kuap were due to kernel bloat pushing >>>> prom_init calls to be done via the plt. Because we did not have >>>> a relocatable kernel, and they are done very early, this caused >>>> everything to explode. Compile with CONFIG_RELOCATABLE! >>>> --- >>>> Documentation/dev-tools/kasan.rst | 8 +- >>>> Documentation/powerpc/kasan.txt | 112 ++++++++++++++++++- >>>> arch/powerpc/Kconfig | 2 + >>>> arch/powerpc/Kconfig.debug | 21 ++++ >>>> arch/powerpc/Makefile | 11 ++ >>>> arch/powerpc/include/asm/book3s/64/hash.h | 4 + >>>> arch/powerpc/include/asm/book3s/64/pgtable.h | 7 ++ >>>> arch/powerpc/include/asm/book3s/64/radix.h | 5 + >>>> arch/powerpc/include/asm/kasan.h | 21 +++- >>>> arch/powerpc/kernel/prom.c | 61 +++++++++- >>>> arch/powerpc/mm/kasan/Makefile | 1 + >>>> arch/powerpc/mm/kasan/init_book3s_64.c | 70 ++++++++++++ >>>> arch/powerpc/platforms/Kconfig.cputype | 1 + >>>> 13 files changed, 316 insertions(+), 8 deletions(-) >>>> create mode 100644 arch/powerpc/mm/kasan/init_book3s_64.c >>>> >>>> diff --git a/arch/powerpc/include/asm/kasan.h b/arch/powerpc/include/asm/kasan.h >>>> index 296e51c2f066..f18268cbdc33 100644 >>>> --- a/arch/powerpc/include/asm/kasan.h >>>> +++ b/arch/powerpc/include/asm/kasan.h >>>> @@ -2,6 +2,9 @@ >>>> #ifndef __ASM_KASAN_H >>>> #define __ASM_KASAN_H >>>> >>>> +#include <asm/page.h> >>>> +#include <asm/pgtable.h> >>> >>> What do you need asm/pgtable.h for ? >>> >>> Build failure due to circular inclusion of asm/pgtable.h: >> >> I see there's a lot of ppc32 stuff, I clearly need to bite the bullet >> and get a ppc32 toolchain so I can squash these without chewing up any >> more of your time. I'll sort that out and send a new spin. >> > > I'm using a powerpc64 toolchain to build both ppc32 and ppc64 kernels > (from https://mirrors.edge.kernel.org/pub/tools/crosstool/ ) I am now using the distro toolchain that Ubuntu provides, and I've reproduced and fixed the 32bit issues you identifed. > Another thing, did you test PTDUMP stuff with KASAN ? It looks like > KASAN address markers don't depend on PPC32, but are only initialised by > populate_markers() for PPC32. Hmm, OK. This is my last workday for the year, so I will look at this and the simplifications to kasan.h early next year. Thanks, Daniel > > Regarding kasan.h, I think we should be able to end up with something > where the definition of KASAN_SHADOW_OFFSET should only depend on the > existence of CONFIG_KASAN_SHADOW_OFFSET, and where only > KASAN_SHADOW_SIZE should depend on the target (ie PPC32 or BOOK3S64) > Everything else should be common. KASAN_END should be START+SIZE. > > It looks like what you have called KASAN_SHADOW_SIZE is not similar to > what is called KASAN_SHADOW_SIZE for PPC32, as yours only covers the > SHADOW_SIZE for linear mem while PPC32 one covers the full space. > > Christophe
