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Minimum version of binutils required to compile the kernel is 2.25.
This version correctly handles the "rep" prefixes, so it is possible
to remove the semicolon, which was used to support ancient versions
of GNU as.
Due to the semicolon, the compiler considers "rep; insn" (or its
alternate "rep\n\tinsn" form) as two separate instructions. Removing
the semicolon makes asm length calculations more accurate, consequently
making scheduling and inlining decisions of the compiler more accurate.
Removing the semicolon also enables assembler checks involving "rep"
prefixes. Trying to assemble e.g. "rep addl %eax, %ebx" results in:
Error: invalid instruction `add' after `rep'
Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Pavel Machek <pavel@kernel.org>
Cc: Rafael J. Wysocki <rafael@kernel.org>
Link: https://lore.kernel.org/r/20250418071437.4144391-2-ubizjak@gmail.com
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The percpu section is currently linked at absolute address 0, because
older compilers hard-coded the stack protector canary value at a fixed
offset from the start of the GS segment. Now that the canary is a
normal percpu variable, the percpu section does not need to be linked
at a specific address.
x86-64 will now calculate the percpu offsets as the delta between the
initial percpu address and the dynamically allocated memory, like other
architectures. Note that GSBASE is limited to the canonical address
width (48 or 57 bits, sign-extended). As long as the kernel text,
modules, and the dynamically allocated percpu memory are all in the
negative address space, the delta will not overflow this limit.
Signed-off-by: Brian Gerst <brgerst@gmail.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Ard Biesheuvel <ardb@kernel.org>
Reviewed-by: Uros Bizjak <ubizjak@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: https://lore.kernel.org/r/20250123190747.745588-9-brgerst@gmail.com
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Instead of having a private area for the stack canary, use
fixed_percpu_data for GSBASE like the native kernel.
Signed-off-by: Brian Gerst <brgerst@gmail.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Ard Biesheuvel <ardb@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: https://lore.kernel.org/r/20250123190747.745588-5-brgerst@gmail.com
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The .head.text section contains code that may execute from a different
address than it was linked at. This is fragile, given that the x86 ABI
can refer to global symbols via absolute or relative references, and the
toolchain assumes that these are interchangeable, which they are not in
this particular case.
For this reason, all absolute symbol references are being removed from
code that is emitted into .head.text. Subsequently, build time
validation may be added that ensures that no absolute ELF relocations
exist at all in that ELF section.
In the case of the PVH code, the absolute references are in 32-bit code,
which gets emitted with R_X86_64_32 relocations, and these are even more
problematic going forward, as it prevents running the linker in PIE
mode.
So update the 64-bit code to avoid _pa(), and to only rely on relative
symbol references: these are always 32-bits wide, even in 64-bit code,
and are resolved by the linker at build time.
Reviewed-by: Jason Andryuk <jason.andryuk@amd.com>
Tested-by: Jason Andryuk <jason.andryuk@amd.com>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Message-ID: <20241009160438.3884381-12-ardb+git@google.com>
Signed-off-by: Juergen Gross <jgross@suse.com>
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Xen puts virtual and physical addresses into ELF notes that are treated
by the linker as relocatable by default. Doing so is not only pointless,
given that the ELF notes are only intended for consumption by Xen before
the kernel boots. It is also a KASLR leak, given that the kernel's ELF
notes are exposed via the world readable /sys/kernel/notes.
So emit these constants in a way that prevents the linker from marking
them as relocatable. This involves place-relative relocations (which
subtract their own virtual address from the symbol value) and linker
provided absolute symbols that add the address of the place to the
desired value.
Tested-by: Jason Andryuk <jason.andryuk@amd.com>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Reviewed-by: Jason Andryuk <jason.andryuk@amd.com>
Message-ID: <20241009160438.3884381-11-ardb+git@google.com>
Signed-off-by: Juergen Gross <jgross@suse.com>
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Since commit
d9ec1158056b ("x86/boot/64: Use RIP_REL_REF() to assign 'phys_base'")
phys_base is assigned directly rather than added to, so it is no longer
necessary to clear it after use.
Reviewed-by: Jason Andryuk <jason.andryuk@amd.com>
Tested-by: Jason Andryuk <jason.andryuk@amd.com>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Message-ID: <20241009160438.3884381-10-ardb+git@google.com>
Signed-off-by: Juergen Gross <jgross@suse.com>
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The limit field in a GDT descriptor is an inclusive bound, and therefore
one less than the size of the covered range.
Reviewed-by: Jason Andryuk <jason.andryuk@amd.com>
Tested-by: Jason Andryuk <jason.andryuk@amd.com>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Message-ID: <20241009160438.3884381-9-ardb+git@google.com>
Signed-off-by: Juergen Gross <jgross@suse.com>
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Calling C code via a different mapping than it was linked at is
problematic, because the compiler assumes that RIP-relative and absolute
symbol references are interchangeable. GCC in particular may use
RIP-relative per-CPU variable references even when not using -fpic.
So call xen_prepare_pvh() via its kernel virtual mapping on x86_64, so
that those RIP-relative references produce the correct values. This
matches the pre-existing behavior for i386, which also invokes
xen_prepare_pvh() via the kernel virtual mapping before invoking
startup_32 with paging disabled again.
Fixes: 7243b93345f7 ("xen/pvh: Bootstrap PVH guest")
Tested-by: Jason Andryuk <jason.andryuk@amd.com>
Reviewed-by: Jason Andryuk <jason.andryuk@amd.com>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Message-ID: <20241009160438.3884381-8-ardb+git@google.com>
Signed-off-by: Juergen Gross <jgross@suse.com>
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The PVH entry point is 32bit. For a 64bit kernel, the entry point must
switch to 64bit mode, which requires a set of page tables. In the past,
PVH used init_top_pgt.
This works fine when the kernel is loaded at LOAD_PHYSICAL_ADDR, as the
page tables are prebuilt for this address. If the kernel is loaded at a
different address, they need to be adjusted.
__startup_64() adjusts the prebuilt page tables for the physical load
address, but it is 64bit code. The 32bit PVH entry code can't call it
to adjust the page tables, so it can't readily be re-used.
64bit PVH entry needs page tables set up for identity map, the kernel
high map and the direct map. pvh_start_xen() enters identity mapped.
Inside xen_prepare_pvh(), it jumps through a pv_ops function pointer
into the highmap. The direct map is used for __va() on the initramfs
and other guest physical addresses.
Add a dedicated set of prebuild page tables for PVH entry. They are
adjusted in assembly before loading.
Add XEN_ELFNOTE_PHYS32_RELOC to indicate support for relocation
along with the kernel's loading constraints. The maximum load address,
KERNEL_IMAGE_SIZE - 1, is determined by a single pvh_level2_ident_pgt
page. It could be larger with more pages.
Signed-off-by: Jason Andryuk <jason.andryuk@amd.com>
Reviewed-by: Juergen Gross <jgross@suse.com>
Message-ID: <20240823193630.2583107-6-jason.andryuk@amd.com>
Signed-off-by: Juergen Gross <jgross@suse.com>
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phys_base needs to be set for __pa() to work in xen_pvh_init() when
finding the hypercall page. Set it before calling into
xen_prepare_pvh(), which calls xen_pvh_init(). Clear it afterward to
avoid __startup_64() adding to it and creating an incorrect value.
Signed-off-by: Jason Andryuk <jason.andryuk@amd.com>
Reviewed-by: Juergen Gross <jgross@suse.com>
Message-ID: <20240823193630.2583107-4-jason.andryuk@amd.com>
Signed-off-by: Juergen Gross <jgross@suse.com>
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The PVH entrypoint is 32bit non-PIC code running the uncompressed
vmlinux at its load address CONFIG_PHYSICAL_START - default 0x1000000
(16MB). The kernel is loaded at that physical address inside the VM by
the VMM software (Xen/QEMU).
When running a Xen PVH Dom0, the host reserved addresses are mapped 1-1
into the PVH container. There exist system firmwares (Coreboot/EDK2)
with reserved memory at 16MB. This creates a conflict where the PVH
kernel cannot be loaded at that address.
Modify the PVH entrypoint to be position-indepedent to allow flexibility
in load address. Only the 64bit entry path is converted. A 32bit
kernel is not PIC, so calling into other parts of the kernel, like
xen_prepare_pvh() and mk_pgtable_32(), don't work properly when
relocated.
This makes the code PIC, but the page tables need to be updated as well
to handle running from the kernel high map.
The UNWIND_HINT_END_OF_STACK is to silence:
vmlinux.o: warning: objtool: pvh_start_xen+0x7f: unreachable instruction
after the lret into 64bit code.
Signed-off-by: Jason Andryuk <jason.andryuk@amd.com>
Reviewed-by: Juergen Gross <jgross@suse.com>
Message-ID: <20240823193630.2583107-3-jason.andryuk@amd.com>
Signed-off-by: Juergen Gross <jgross@suse.com>
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git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull x86 cleanups from Ingo Molnar:
- Change global variables to local
- Add missing kernel-doc function parameter descriptions
- Remove unused parameter from a macro
- Remove obsolete Kconfig entry
- Fix comments
- Fix typos, mostly scripted, manually reviewed
and a micro-optimization got misplaced as a cleanup:
- Micro-optimize the asm code in secondary_startup_64_no_verify()
* tag 'x86-cleanups-2024-01-08' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
arch/x86: Fix typos
x86/head_64: Use TESTB instead of TESTL in secondary_startup_64_no_verify()
x86/docs: Remove reference to syscall trampoline in PTI
x86/Kconfig: Remove obsolete config X86_32_SMP
x86/io: Remove the unused 'bw' parameter from the BUILDIO() macro
x86/mtrr: Document missing function parameters in kernel-doc
x86/setup: Make relocated_ramdisk a local variable of relocate_initrd()
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Fix typos, most reported by "codespell arch/x86". Only touches comments,
no code changes.
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Randy Dunlap <rdunlap@infradead.org>
Link: https://lore.kernel.org/r/20240103004011.1758650-1-helgaas@kernel.org
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Actually replace the numeric values by the new symbolic values.
I used this to find all the existing users of the GDT_ENTRY*() macros:
$ git grep -P 'GDT_ENTRY(_INIT)?\('
Some of the lines will exceed 80 characters, but some of them will be
shorter again in the next couple of patches.
Signed-off-by: Vegard Nossum <vegard.nossum@oracle.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Link: https://lore.kernel.org/r/20231219151200.2878271-4-vegard.nossum@oracle.com
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We'd like to replace all the magic numbers in various GDT descriptors
with new, semantically meaningful, symbolic values.
In order to be able to verify that the change doesn't cause any actual
changes to the compiled binary code, I've split the change into two
patches:
- Part 1 (this commit): everything _but_ actually replacing the numbers
- Part 2 (the following commit): _only_ replacing the numbers
The reason we need this split for verification is that including new
headers causes some spurious changes to the object files, mostly line
number changes in the debug info but occasionally other subtle codegen
changes.
Signed-off-by: Vegard Nossum <vegard.nossum@oracle.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Link: https://lore.kernel.org/r/20231219151200.2878271-3-vegard.nossum@oracle.com
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Mark reported that the ORC unwinder incorrectly marks an unwind as
reliable when the unwind terminates prematurely in the dark corners of
return_to_handler() due to lack of information about the next frame.
The problem is UNWIND_HINT_EMPTY is used in two different situations:
1) The end of the kernel stack unwind before hitting user entry, boot
code, or fork entry
2) A blind spot in ORC coverage where the unwinder has to bail due to
lack of information about the next frame
The ORC unwinder has no way to tell the difference between the two.
When it encounters an undefined stack state with 'end=1', it blindly
marks the stack reliable, which can break the livepatch consistency
model.
Fix it by splitting UNWIND_HINT_EMPTY into UNWIND_HINT_UNDEFINED and
UNWIND_HINT_END_OF_STACK.
Reported-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/fd6212c8b450d3564b855e1cb48404d6277b4d9f.1677683419.git.jpoimboe@kernel.org
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SYM_CODE_START*() doesn't get auto-validated and needs an UNWIND hint
to get checked, add one.
vmlinux.o: warning: objtool: pvh_start_xen()+0x0: unreachable
Reported-by: Thomas Gleixner <tglx@linutronix.de>
Reported-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Link: https://lore.kernel.org/r/20220408094718.321246297@infradead.org
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git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull x86 updates from Borislav Petkov:
- Turn the stack canary into a normal __percpu variable on 32-bit which
gets rid of the LAZY_GS stuff and a lot of code.
- Add an insn_decode() API which all users of the instruction decoder
should preferrably use. Its goal is to keep the details of the
instruction decoder away from its users and simplify and streamline
how one decodes insns in the kernel. Convert its users to it.
- kprobes improvements and fixes
- Set the maximum DIE per package variable on Hygon
- Rip out the dynamic NOP selection and simplify all the machinery
around selecting NOPs. Use the simplified NOPs in objtool now too.
- Add Xeon Sapphire Rapids to list of CPUs that support PPIN
- Simplify the retpolines by folding the entire thing into an
alternative now that objtool can handle alternatives with stack ops.
Then, have objtool rewrite the call to the retpoline with the
alternative which then will get patched at boot time.
- Document Intel uarch per models in intel-family.h
- Make Sub-NUMA Clustering topology the default and Cluster-on-Die the
exception on Intel.
* tag 'x86_core_for_v5.13' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (53 commits)
x86, sched: Treat Intel SNC topology as default, COD as exception
x86/cpu: Comment Skylake server stepping too
x86/cpu: Resort and comment Intel models
objtool/x86: Rewrite retpoline thunk calls
objtool: Skip magical retpoline .altinstr_replacement
objtool: Cache instruction relocs
objtool: Keep track of retpoline call sites
objtool: Add elf_create_undef_symbol()
objtool: Extract elf_symbol_add()
objtool: Extract elf_strtab_concat()
objtool: Create reloc sections implicitly
objtool: Add elf_create_reloc() helper
objtool: Rework the elf_rebuild_reloc_section() logic
objtool: Fix static_call list generation
objtool: Handle per arch retpoline naming
objtool: Correctly handle retpoline thunk calls
x86/retpoline: Simplify retpolines
x86/alternatives: Optimize optimize_nops()
x86: Add insn_decode_kernel()
x86/kprobes: Move 'inline' to the beginning of the kprobe_is_ss() declaration
...
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We've accumulated a few unusual Unicode characters in arch/x86/
over the years, substitute them with their proper ASCII equivalents.
A few of them were a whitespace equivalent: ' ' - the use was harmless.
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: linux-kernel@vger.kernel.org
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On 32-bit kernels, the stackprotector canary is quite nasty -- it is
stored at %gs:(20), which is nasty because 32-bit kernels use %fs for
percpu storage. It's even nastier because it means that whether %gs
contains userspace state or kernel state while running kernel code
depends on whether stackprotector is enabled (this is
CONFIG_X86_32_LAZY_GS), and this setting radically changes the way
that segment selectors work. Supporting both variants is a
maintenance and testing mess.
Merely rearranging so that percpu and the stack canary
share the same segment would be messy as the 32-bit percpu address
layout isn't currently compatible with putting a variable at a fixed
offset.
Fortunately, GCC 8.1 added options that allow the stack canary to be
accessed as %fs:__stack_chk_guard, effectively turning it into an ordinary
percpu variable. This lets us get rid of all of the code to manage the
stack canary GDT descriptor and the CONFIG_X86_32_LAZY_GS mess.
(That name is special. We could use any symbol we want for the
%fs-relative mode, but for CONFIG_SMP=n, gcc refuses to let us use any
name other than __stack_chk_guard.)
Forcibly disable stackprotector on older compilers that don't support
the new options and turn the stack canary into a percpu variable. The
"lazy GS" approach is now used for all 32-bit configurations.
Also makes load_gs_index() work on 32-bit kernels. On 64-bit kernels,
it loads the GS selector and updates the user GSBASE accordingly. (This
is unchanged.) On 32-bit kernels, it loads the GS selector and updates
GSBASE, which is now always the user base. This means that the overall
effect is the same on 32-bit and 64-bit, which avoids some ifdeffery.
[ bp: Massage commit message. ]
Signed-off-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/c0ff7dba14041c7e5d1cae5d4df052f03759bef3.1613243844.git.luto@kernel.org
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This indirect jump is harmless; annotate it to keep objtool's retpoline
validation happy.
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Juergen Gross <jgross@suse.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Reviewed-by: Juergen Gross <jgross@suse.com>
Link: https://lore.kernel.org/r/4797c72a258b26e06741c58ccd4a75c42db39c1d.1611263462.git.jpoimboe@redhat.com
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There are a couple of assembly functions which are invoked only locally
in the file they are defined. In C, they are marked "static". In
assembly, annotate them using SYM_{FUNC,CODE}_START_LOCAL (and switch
their ENDPROC to SYM_{FUNC,CODE}_END too). Whether FUNC or CODE is used,
depends on whether ENDPROC or END was used for a particular function
before.
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Signed-off-by: Borislav Petkov <bp@suse.de>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Andy Shevchenko <andy@infradead.org>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Darren Hart <dvhart@infradead.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: linux-arch@vger.kernel.org
Cc: linux-efi <linux-efi@vger.kernel.org>
Cc: linux-efi@vger.kernel.org
Cc: Matt Fleming <matt@codeblueprint.co.uk>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: platform-driver-x86@vger.kernel.org
Cc: Stefano Stabellini <sstabellini@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: x86-ml <x86@kernel.org>
Cc: xen-devel@lists.xenproject.org
Link: https://lkml.kernel.org/r/20191011115108.12392-21-jslaby@suse.cz
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Use the new SYM_DATA_START_LOCAL, and SYM_DATA_END* macros to get:
0000 8 OBJECT LOCAL DEFAULT 6 gdt
0008 32 OBJECT LOCAL DEFAULT 6 gdt_start
0028 0 OBJECT LOCAL DEFAULT 6 gdt_end
0028 256 OBJECT LOCAL DEFAULT 6 early_stack
0128 0 OBJECT LOCAL DEFAULT 6 early_stack
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Andy Shevchenko <andy@infradead.org>
Cc: Darren Hart <dvhart@infradead.org>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: linux-arch@vger.kernel.org
Cc: platform-driver-x86@vger.kernel.org
Cc: Stefano Stabellini <sstabellini@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: x86-ml <x86@kernel.org>
Cc: xen-devel@lists.xenproject.org
Link: https://lkml.kernel.org/r/20191011115108.12392-15-jslaby@suse.cz
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Once hypervisors other than Xen start using the PVH entry point for
starting VMs, we would like the option of being able to compile PVH entry
capable kernels without enabling CONFIG_XEN and all the code that comes
along with that. To allow that, we are moving the PVH code out of Xen and
into files sitting at a higher level in the tree.
This patch is not introducing any code or functional changes, just moving
files from one location to another.
Signed-off-by: Maran Wilson <maran.wilson@oracle.com>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Reviewed-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
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