Re: [PATCH] powerpc: disable support for relative ksymtab references
From: Nicholas Piggin <hidden>
Date: 2018-08-29 08:09:32
Also in:
linuxppc-dev
On Wed, 29 Aug 2018 08:47:53 +0200 Ard Biesheuvel [off-list ref] wrote:
The newly added code that emits ksymtab entries as pairs of 32-bit relative references interacts poorly with the way powerpc lays out its address space: when a module exports a per-CPU variable, the primary module region covering the ksymtab entry -and thus the 32-bit relative reference- is too far away from the actual per-CPU variable's base address (to which the per-CPU offsets are applied to obtain the respective address of each CPU's copy), resulting in corruption when the module loader attempts to resolve symbol references of modules that are loaded on top and link to the exported per-CPU symbol. So let's disable this feature on powerpc. Even though it implements CONFIG_RELOCATABLE, it does not implement CONFIG_RANDOMIZE_BASE and so KASLR kernels (which are the main target of the feature) do not exist on powerpc anyway.
Let's go with this for now. We have a bit more work to do with module loader, linker, percpu, or all of the above. Thanks everyone. Linus can you merge this? I think Michael is on vacation this week and things are pretty crashy without it here. Don't need to call him off the beach for it. Thanks, Nick
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Reported-by: Andreas Schwab <redacted> Suggested-by: Nicholas Piggin <redacted> Signed-off-by: Ard Biesheuvel <redacted> --- arch/powerpc/Kconfig | 1 - 1 file changed, 1 deletion(-)diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig index db0b6eebbfa5..a80669209155 100644 --- a/arch/powerpc/Kconfig +++ b/arch/powerpc/Kconfig@@ -177,7 +177,6 @@ config PPC select HAVE_ARCH_KGDB select HAVE_ARCH_MMAP_RND_BITS select HAVE_ARCH_MMAP_RND_COMPAT_BITS if COMPAT - select HAVE_ARCH_PREL32_RELOCATIONS select HAVE_ARCH_SECCOMP_FILTER select HAVE_ARCH_TRACEHOOK select HAVE_CBPF_JIT if !PPC64-- 2.17.1