Re: [PATCH RFC v2 02/29] x86: Create CONFIG_MITIGATION_ADDRESS_SPACE_ISOLATION
From: Mike Rapoport <rppt@kernel.org>
Date: 2025-03-01 07:24:30
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kvm, linux-alpha, linux-arch, linux-efi, linux-m68k, linux-mips, linux-mm, linux-perf-users, linux-riscv, linux-s390, linux-sh, linux-trace-kernel, linux-um, lkml, loongarch, sparclinux
Hi Brendan, On Fri, Jan 10, 2025 at 06:40:28PM +0000, Brendan Jackman wrote:
Currently a nop config. Keeping as a separate commit for easy review of the boring bits. Later commits will use and enable this new config. This config is only added for non-UML x86_64 as other architectures do not yet have pending implementations. It also has somewhat artificial dependencies on !PARAVIRT and !KASAN which are explained in the Kconfig file. Co-developed-by: Junaid Shahid <redacted> Signed-off-by: Junaid Shahid <redacted> Signed-off-by: Brendan Jackman <jackmanb@google.com> --- arch/alpha/include/asm/Kbuild | 1 + arch/arc/include/asm/Kbuild | 1 + arch/arm/include/asm/Kbuild | 1 + arch/arm64/include/asm/Kbuild | 1 + arch/csky/include/asm/Kbuild | 1 + arch/hexagon/include/asm/Kbuild | 1 + arch/loongarch/include/asm/Kbuild | 3 +++ arch/m68k/include/asm/Kbuild | 1 + arch/microblaze/include/asm/Kbuild | 1 + arch/mips/include/asm/Kbuild | 1 + arch/nios2/include/asm/Kbuild | 1 + arch/openrisc/include/asm/Kbuild | 1 + arch/parisc/include/asm/Kbuild | 1 + arch/powerpc/include/asm/Kbuild | 1 + arch/riscv/include/asm/Kbuild | 1 + arch/s390/include/asm/Kbuild | 1 + arch/sh/include/asm/Kbuild | 1 + arch/sparc/include/asm/Kbuild | 1 + arch/um/include/asm/Kbuild | 2 +- arch/x86/Kconfig | 14 ++++++++++++++ arch/xtensa/include/asm/Kbuild | 1 + include/asm-generic/asi.h | 5 +++++ 22 files changed, 41 insertions(+), 1 deletion(-)
I don't think this all is needed. You can put asi.h with stubs used outside of arch/x86 in include/linux and save you the hassle of updating every architecture.
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diff --git a/arch/sparc/include/asm/Kbuild b/arch/sparc/include/asm/Kbuild index 43b0ae4c2c2112d4d4d3cb3c60e787b175172dea..cb9062c9be17fe276cc92d2ac99d8b165f6297bf 100644 --- a/arch/sparc/include/asm/Kbuild +++ b/arch/sparc/include/asm/Kbuild@@ -4,3 +4,4 @@ generated-y += syscall_table_64.h generic-y += agp.h generic-y += kvm_para.h generic-y += mcs_spinlock.h +generic-y += asi.h
sparc already has include/asm/asi.h, this will break the build
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diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig index 7b9a7e8f39acc8e9aeb7d4213e87d71047865f5c..5a50582eb210e9d1309856a737d32b76fa1bfc85 100644 --- a/arch/x86/Kconfig +++ b/arch/x86/Kconfig@@ -2519,6 +2519,20 @@ config MITIGATION_PAGE_TABLE_ISOLATION See Documentation/arch/x86/pti.rst for more details. +config MITIGATION_ADDRESS_SPACE_ISOLATION + bool "Allow code to run with a reduced kernel address space" + default n + depends on X86_64 && !PARAVIRT && !UML + help + This feature provides the ability to run some kernel code + with a reduced kernel address space. This can be used to + mitigate some speculative execution attacks. + + The !PARAVIRT dependency is only because of lack of testing; in theory + the code is written to work under paravirtualization. In practice + there are likely to be unhandled cases, in particular concerning TLB + flushes. +
If you expect other architectures might implement ASI the config would better fit into init/Kconfig or mm/Kconfig and in arch/x86/Kconfig will define ARCH_HAS_MITIGATION_ADDRESS_SPACE_ISOLATION.
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config MITIGATION_RETPOLINE bool "Avoid speculative indirect branches in kernel" select OBJTOOL if HAVE_OBJTOOLdiff --git a/arch/xtensa/include/asm/Kbuild b/arch/xtensa/include/asm/Kbuild index fa07c686cbcc2153776a478ac4093846f01eddab..07cea6902f98053be244d026ed594fe7246755a6 100644 --- a/arch/xtensa/include/asm/Kbuild +++ b/arch/xtensa/include/asm/Kbuild@@ -8,3 +8,4 @@ generic-y += parport.h generic-y += qrwlock.h generic-y += qspinlock.h generic-y += user.h +generic-y += asi.hdiff --git a/include/asm-generic/asi.h b/include/asm-generic/asi.h new file mode 100644 index 0000000000000000000000000000000000000000..c4d9a5ff860a96428422a15000c622aeecc2d664 --- /dev/null +++ b/include/asm-generic/asi.h@@ -0,0 +1,5 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +#ifndef __ASM_GENERIC_ASI_H +#define __ASM_GENERIC_ASI_H + +#endif
IMHO it should be include/linux/asi.h, with something like #infdef __LINUX_ASI_H #define __LINUX_ASI_H #ifdef CONFIG_MITIGATION_ADDRESS_SPACE_ISOLATION #include <asm/asi.h> #else /* CONFIG_MITIGATION_ADDRESS_SPACE_ISOLATION */ /* stubs for functions used outside arch/ */ #endif /* CONFIG_MITIGATION_ADDRESS_SPACE_ISOLATION */ #endif /* __LINUX_ASI_H */ -- Sincerely yours, Mike.