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ANNOTATE_IGNORE_ALTERNATIVE adds additional noise to the code generated
by CLAC/STAC alternatives, hurting readability for those whose read
uaccess-related code generation on a regular basis.
Remove the annotation specifically for the "NOP patched with CLAC/STAC"
case in favor of a manual check.
Leave the other uses of that annotation in place as they're less common
and more difficult to detect.
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Link: https://lore.kernel.org/r/fc972ba4995d826fcfb8d02733a14be8d670900b.1744098446.git.jpoimboe@kernel.org
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For X86_FEATURE_SMAP alternatives which replace NOP with STAC or CLAC,
uaccess validation skips the NOP branch to avoid following impossible
code paths, e.g. where a STAC would be patched but a CLAC wouldn't.
However, it's not safe to assume an X86_FEATURE_SMAP alternative is
patching STAC/CLAC. There can be other alternatives, like
static_cpu_has(), where both branches need to be validated.
Fix that by repurposing ANNOTATE_IGNORE_ALTERNATIVE for skipping either
original instructions or new ones. This is a more generic approach
which enables the removal of the feature checking hacks and the
insn->ignore bit.
Fixes the following warnings:
arch/x86/mm/fault.o: warning: objtool: do_user_addr_fault+0x8ec: __stack_chk_fail() missing __noreturn in .c/.h or NORETURN() in noreturns.h
arch/x86/mm/fault.o: warning: objtool: do_user_addr_fault+0x8f1: unreachable instruction
[ mingo: Fix up conflicts with recent x86 changes. ]
Fixes: ea24213d8088 ("objtool: Add UACCESS validation")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: https://lore.kernel.org/r/de0621ca242130156a55d5d74fed86994dfa4c9c.1742852846.git.jpoimboe@kernel.org
Closes: https://lore.kernel.org/oe-kbuild-all/202503181736.zkZUBv4N-lkp@intel.com/
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While the GCC and Clang compilers already define __ASSEMBLER__
automatically when compiling assembly code, __ASSEMBLY__ is a
macro that only gets defined by the Makefiles in the kernel.
This can be very confusing when switching between userspace
and kernelspace coding, or when dealing with UAPI headers that
rather should use __ASSEMBLER__ instead. So let's standardize on
the __ASSEMBLER__ macro that is provided by the compilers now.
This is mostly a mechanical patch (done with a simple "sed -i"
statement), with some manual tweaks in <asm/frame.h>, <asm/hw_irq.h>
and <asm/setup.h> that mentioned this macro in comments with some
missing underscores.
Signed-off-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: https://lore.kernel.org/r/20250314071013.1575167-38-thuth@redhat.com
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Back when we added SMAP support, all versions of binutils didn't
necessarily understand the 'clac' and 'stac' instructions. So we
implemented those instructions manually as ".byte" sequences.
But we've since upgraded the minimum version of binutils to version
2.25, and that included proper support for the SMAP instructions, and
there's no reason for us to use some line noise to express them any
more.
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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Those were added as part of the SMAP enablement but SMAP is currently
an integral part of kernel proper and there's no need to disable it
anymore.
Rip out that functionality. Leave --uaccess default on for objtool as
this is what objtool should do by default anyway.
If still needed - clearcpuid=smap.
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Lai Jiangshan <jiangshanlai@gmail.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20220127115626.14179-4-bp@alien8.de
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git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull x86 alternatives/paravirt updates from Borislav Petkov:
"First big cleanup to the paravirt infra to use alternatives and thus
eliminate custom code patching.
For that, the alternatives infrastructure is extended to accomodate
paravirt's needs and, as a result, a lot of paravirt patching code
goes away, leading to a sizeable cleanup and simplification.
Work by Juergen Gross"
* tag 'x86_alternatives_for_v5.13' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
x86/paravirt: Have only one paravirt patch function
x86/paravirt: Switch functions with custom code to ALTERNATIVE
x86/paravirt: Add new PVOP_ALT* macros to support pvops in ALTERNATIVEs
x86/paravirt: Switch iret pvops to ALTERNATIVE
x86/paravirt: Simplify paravirt macros
x86/paravirt: Remove no longer needed 32-bit pvops cruft
x86/paravirt: Add new features for paravirt patching
x86/alternative: Use ALTERNATIVE_TERNARY() in _static_cpu_has()
x86/alternative: Support ALTERNATIVE_TERNARY
x86/alternative: Support not-feature
x86/paravirt: Switch time pvops functions to use static_call()
static_call: Add function to query current function
static_call: Move struct static_call_key definition to static_call_types.h
x86/alternative: Merge include files
x86/alternative: Drop unused feature parameter from ALTINSTR_REPLACEMENT()
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Commit ab234a260b1f ("x86/pv: Rework arch_local_irq_restore() to not
use popf") replaced "push %reg; popf" with something like: "test
$0x200, %reg; jz 1f; sti; 1:", which breaks the pushf/popf symmetry
that commit ea24213d8088 ("objtool: Add UACCESS validation") relies
on.
The result is:
drivers/gpu/drm/amd/amdgpu/si.o: warning: objtool: si_common_hw_init()+0xf36: PUSHF stack exhausted
Meanwhile, commit c9c324dc22aa ("objtool: Support stack layout changes
in alternatives") makes that we can actually use stack-ops in
alternatives, which means we can revert 1ff865e343c2 ("x86,smap: Fix
smap_{save,restore}() alternatives").
That in turn means we can limit the PUSHF/POPF handling of
ea24213d8088 to those instructions that are in alternatives.
Fixes: ab234a260b1f ("x86/pv: Rework arch_local_irq_restore() to not use popf")
Reported-by: Borislav Petkov <bp@alien8.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Link: https://lkml.kernel.org/r/YEY4rIbQYa5fnnEp@hirez.programming.kicks-ass.net
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Merge arch/x86/include/asm/alternative-asm.h into
arch/x86/include/asm/alternative.h in order to make it easier to use
common definitions later.
Signed-off-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20210311142319.4723-2-jgross@suse.com
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As reported by objtool:
lib/ubsan.o: warning: objtool: .altinstr_replacement+0x0: alternative modifies stack
lib/ubsan.o: warning: objtool: .altinstr_replacement+0x7: alternative modifies stack
the smap_{save,restore}() alternatives violate (the newly enforced)
rule on stack invariance. That is, due to there only being a single
ORC table it must be valid to any alternative. These alternatives
violate this with the direct result that unwinds will not be correct
when it hits between the PUSH and POP instructions.
Rewrite the functions to only have a conditional jump.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Miroslav Benes <mbenes@suse.cz>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Link: https://lkml.kernel.org/r/20200429101802.GI13592@hirez.programming.kicks-ass.net
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Based on 1 normalized pattern(s):
this program is free software you can redistribute it and or modify
it under the terms of the gnu general public license as published by
the free software foundation version 2 of the license
extracted by the scancode license scanner the SPDX license identifier
GPL-2.0-only
has been chosen to replace the boilerplate/reference in 315 file(s).
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Allison Randal <allison@lohutok.net>
Reviewed-by: Armijn Hemel <armijn@tjaldur.nl>
Cc: linux-spdx@vger.kernel.org
Link: https://lkml.kernel.org/r/20190531190115.503150771@linutronix.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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Linus noticed all users of __ASM_STAC/__ASM_CLAC are with
__stringify(). Just make them a string.
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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Introduce common helpers for when we need to safely suspend a
uaccess section; for instance to generate a {KA,UB}SAN report.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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Move them to a separate header and have the following
dependency:
x86/cpufeatures.h <- x86/processor.h <- x86/cpufeature.h
This makes it easier to use the header in asm code and not
include the whole cpufeature.h and add guards for asm.
Suggested-by: H. Peter Anvin <hpa@zytor.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1453842730-28463-5-git-send-email-bp@alien8.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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... and drop unfolded version. No need for ASM_NOP3 anymore either as
the alternatives do the proper padding at build time and insert proper
NOPs at boot time.
There should be no apparent operational change from this patch.
Signed-off-by: Borislav Petkov <bp@suse.de>
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Up until now we have always paid attention to make sure the length of
the new instruction replacing the old one is at least less or equal to
the length of the old instruction. If the new instruction is longer, at
the time it replaces the old instruction it will overwrite the beginning
of the next instruction in the kernel image and cause your pants to
catch fire.
So instead of having to pay attention, teach the alternatives framework
to pad shorter old instructions with NOPs at buildtime - but only in the
case when
len(old instruction(s)) < len(new instruction(s))
and add nothing in the >= case. (In that case we do add_nops() when
patching).
This way the alternatives user shouldn't have to care about instruction
sizes and simply use the macros.
Add asm ALTERNATIVE* flavor macros too, while at it.
Also, we need to save the pad length in a separate struct alt_instr
member for NOP optimization and the way to do that reliably is to carry
the pad length instead of trying to detect whether we're looking at
single-byte NOPs or at pathological instruction offsets like e9 90 90 90
90, for example, which is a valid instruction.
Thanks to Michael Matz for the great help with toolchain questions.
Signed-off-by: Borislav Petkov <bp@suse.de>
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When Supervisor Mode Access Prevention (SMAP) is enabled, access to
userspace from the kernel is controlled by the AC flag. To make the
performance of manipulating that flag acceptable, there are two new
instructions, STAC and CLAC, to set and clear it.
This patch adds those instructions, via alternative(), when the SMAP
feature is enabled. It also adds X86_EFLAGS_AC unconditionally to the
SYSCALL entry mask; there is simply no reason to make that one
conditional.
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
Link: http://lkml.kernel.org/r/1348256595-29119-9-git-send-email-hpa@linux.intel.com
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The STAC/CLAC instructions are only available with SMAP, but on the
other hand they aren't needed if SMAP is not available, or before we
start to run userspace, so construct them as alternatives which start
out as noops and are enabled by the alternatives mechanism.
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
Link: http://lkml.kernel.org/r/1348256595-29119-7-git-send-email-hpa@linux.intel.com
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