linux_dsm_epyc7002/arch/arm64/kernel/vmlinux.lds.S
Ard Biesheuvel f7b93d4294 arm64/alternatives: use subsections for replacement sequences
When building very large kernels, the logic that emits replacement
sequences for alternatives fails when relative branches are present
in the code that is emitted into the .altinstr_replacement section
and patched in at the original site and fixed up. The reason is that
the linker will insert veneers if relative branches go out of range,
and due to the relative distance of the .altinstr_replacement from
the .text section where its branch targets usually live, veneers
may be emitted at the end of the .altinstr_replacement section, with
the relative branches in the sequence pointed at the veneers instead
of the actual target.

The alternatives patching logic will attempt to fix up the branch to
point to its original target, which will be the veneer in this case,
but given that the patch site is likely to be far away as well, it
will be out of range and so patching will fail. There are other cases
where these veneers are problematic, e.g., when the target of the
branch is in .text while the patch site is in .init.text, in which
case putting the replacement sequence inside .text may not help either.

So let's use subsections to emit the replacement code as closely as
possible to the patch site, to ensure that veneers are only likely to
be emitted if they are required at the patch site as well, in which
case they will be in range for the replacement sequence both before
and after it is transported to the patch site.

This will prevent alternative sequences in non-init code from being
released from memory after boot, but this is tolerable given that the
entire section is only 512 KB on an allyesconfig build (which weighs in
at 500+ MB for the entire Image). Also, note that modules today carry
the replacement sequences in non-init sections as well, and any of
those that target init code will be emitted into init sections after
this change.

This fixes an early crash when booting an allyesconfig kernel on a
system where any of the alternatives sequences containing relative
branches are activated at boot (e.g., ARM64_HAS_PAN on TX2)

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Cc: Suzuki K Poulose <suzuki.poulose@arm.com>
Cc: James Morse <james.morse@arm.com>
Cc: Andre Przywara <andre.przywara@arm.com>
Cc: Dave P Martin <dave.martin@arm.com>
Link: https://lore.kernel.org/r/20200630081921.13443-1-ardb@kernel.org
Signed-off-by: Will Deacon <will@kernel.org>
2020-07-02 12:57:17 +01:00

271 lines
5.9 KiB
ArmAsm

/* SPDX-License-Identifier: GPL-2.0 */
/*
* ld script to make ARM Linux kernel
* taken from the i386 version by Russell King
* Written by Martin Mares <mj@atrey.karlin.mff.cuni.cz>
*/
#define RO_EXCEPTION_TABLE_ALIGN 8
#include <asm-generic/vmlinux.lds.h>
#include <asm/cache.h>
#include <asm/kernel-pgtable.h>
#include <asm/thread_info.h>
#include <asm/memory.h>
#include <asm/page.h>
#include "image.h"
OUTPUT_ARCH(aarch64)
ENTRY(_text)
jiffies = jiffies_64;
#define HYPERVISOR_TEXT \
/* \
* Align to 4 KB so that \
* a) the HYP vector table is at its minimum \
* alignment of 2048 bytes \
* b) the HYP init code will not cross a page \
* boundary if its size does not exceed \
* 4 KB (see related ASSERT() below) \
*/ \
. = ALIGN(SZ_4K); \
__hyp_idmap_text_start = .; \
*(.hyp.idmap.text) \
__hyp_idmap_text_end = .; \
__hyp_text_start = .; \
*(.hyp.text) \
__hyp_text_end = .;
#define IDMAP_TEXT \
. = ALIGN(SZ_4K); \
__idmap_text_start = .; \
*(.idmap.text) \
__idmap_text_end = .;
#ifdef CONFIG_HIBERNATION
#define HIBERNATE_TEXT \
. = ALIGN(SZ_4K); \
__hibernate_exit_text_start = .; \
*(.hibernate_exit.text) \
__hibernate_exit_text_end = .;
#else
#define HIBERNATE_TEXT
#endif
#ifdef CONFIG_UNMAP_KERNEL_AT_EL0
#define TRAMP_TEXT \
. = ALIGN(PAGE_SIZE); \
__entry_tramp_text_start = .; \
*(.entry.tramp.text) \
. = ALIGN(PAGE_SIZE); \
__entry_tramp_text_end = .;
#else
#define TRAMP_TEXT
#endif
/*
* The size of the PE/COFF section that covers the kernel image, which
* runs from _stext to _edata, must be a round multiple of the PE/COFF
* FileAlignment, which we set to its minimum value of 0x200. '_stext'
* itself is 4 KB aligned, so padding out _edata to a 0x200 aligned
* boundary should be sufficient.
*/
PECOFF_FILE_ALIGNMENT = 0x200;
#ifdef CONFIG_EFI
#define PECOFF_EDATA_PADDING \
.pecoff_edata_padding : { BYTE(0); . = ALIGN(PECOFF_FILE_ALIGNMENT); }
#else
#define PECOFF_EDATA_PADDING
#endif
SECTIONS
{
/*
* XXX: The linker does not define how output sections are
* assigned to input sections when there are multiple statements
* matching the same input section name. There is no documented
* order of matching.
*/
/DISCARD/ : {
EXIT_CALL
*(.discard)
*(.discard.*)
*(.interp .dynamic)
*(.dynsym .dynstr .hash .gnu.hash)
*(.eh_frame)
}
. = KIMAGE_VADDR + TEXT_OFFSET;
.head.text : {
_text = .;
HEAD_TEXT
}
.text : { /* Real text segment */
_stext = .; /* Text and read-only data */
IRQENTRY_TEXT
SOFTIRQENTRY_TEXT
ENTRY_TEXT
TEXT_TEXT
SCHED_TEXT
CPUIDLE_TEXT
LOCK_TEXT
KPROBES_TEXT
HYPERVISOR_TEXT
IDMAP_TEXT
HIBERNATE_TEXT
TRAMP_TEXT
*(.fixup)
*(.gnu.warning)
. = ALIGN(16);
*(.got) /* Global offset table */
}
. = ALIGN(SEGMENT_ALIGN);
_etext = .; /* End of text section */
/* everything from this point to __init_begin will be marked RO NX */
RO_DATA(PAGE_SIZE)
idmap_pg_dir = .;
. += IDMAP_DIR_SIZE;
idmap_pg_end = .;
#ifdef CONFIG_UNMAP_KERNEL_AT_EL0
tramp_pg_dir = .;
. += PAGE_SIZE;
#endif
#ifdef CONFIG_ARM64_SW_TTBR0_PAN
reserved_ttbr0 = .;
. += RESERVED_TTBR0_SIZE;
#endif
swapper_pg_dir = .;
. += PAGE_SIZE;
swapper_pg_end = .;
. = ALIGN(SEGMENT_ALIGN);
__init_begin = .;
__inittext_begin = .;
INIT_TEXT_SECTION(8)
__exittext_begin = .;
.exit.text : {
EXIT_TEXT
}
__exittext_end = .;
. = ALIGN(4);
.altinstructions : {
__alt_instructions = .;
*(.altinstructions)
__alt_instructions_end = .;
}
. = ALIGN(SEGMENT_ALIGN);
__inittext_end = .;
__initdata_begin = .;
.init.data : {
INIT_DATA
INIT_SETUP(16)
INIT_CALLS
CON_INITCALL
INIT_RAM_FS
*(.init.rodata.* .init.bss) /* from the EFI stub */
}
.exit.data : {
EXIT_DATA
}
PERCPU_SECTION(L1_CACHE_BYTES)
.rela.dyn : ALIGN(8) {
*(.rela .rela*)
}
__rela_offset = ABSOLUTE(ADDR(.rela.dyn) - KIMAGE_VADDR);
__rela_size = SIZEOF(.rela.dyn);
#ifdef CONFIG_RELR
.relr.dyn : ALIGN(8) {
*(.relr.dyn)
}
__relr_offset = ABSOLUTE(ADDR(.relr.dyn) - KIMAGE_VADDR);
__relr_size = SIZEOF(.relr.dyn);
#endif
. = ALIGN(SEGMENT_ALIGN);
__initdata_end = .;
__init_end = .;
_data = .;
_sdata = .;
RW_DATA(L1_CACHE_BYTES, PAGE_SIZE, THREAD_ALIGN)
/*
* Data written with the MMU off but read with the MMU on requires
* cache lines to be invalidated, discarding up to a Cache Writeback
* Granule (CWG) of data from the cache. Keep the section that
* requires this type of maintenance to be in its own Cache Writeback
* Granule (CWG) area so the cache maintenance operations don't
* interfere with adjacent data.
*/
.mmuoff.data.write : ALIGN(SZ_2K) {
__mmuoff_data_start = .;
*(.mmuoff.data.write)
}
. = ALIGN(SZ_2K);
.mmuoff.data.read : {
*(.mmuoff.data.read)
__mmuoff_data_end = .;
}
PECOFF_EDATA_PADDING
__pecoff_data_rawsize = ABSOLUTE(. - __initdata_begin);
_edata = .;
BSS_SECTION(0, 0, 0)
. = ALIGN(PAGE_SIZE);
init_pg_dir = .;
. += INIT_DIR_SIZE;
init_pg_end = .;
. = ALIGN(SEGMENT_ALIGN);
__pecoff_data_size = ABSOLUTE(. - __initdata_begin);
_end = .;
STABS_DEBUG
HEAD_SYMBOLS
}
#include "image-vars.h"
/*
* The HYP init code and ID map text can't be longer than a page each,
* and should not cross a page boundary.
*/
ASSERT(__hyp_idmap_text_end - (__hyp_idmap_text_start & ~(SZ_4K - 1)) <= SZ_4K,
"HYP init code too big or misaligned")
ASSERT(__idmap_text_end - (__idmap_text_start & ~(SZ_4K - 1)) <= SZ_4K,
"ID map text too big or misaligned")
#ifdef CONFIG_HIBERNATION
ASSERT(__hibernate_exit_text_end - (__hibernate_exit_text_start & ~(SZ_4K - 1))
<= SZ_4K, "Hibernate exit text too big or misaligned")
#endif
#ifdef CONFIG_UNMAP_KERNEL_AT_EL0
ASSERT((__entry_tramp_text_end - __entry_tramp_text_start) == PAGE_SIZE,
"Entry trampoline text too big")
#endif
/*
* If padding is applied before .head.text, virt<->phys conversions will fail.
*/
ASSERT(_text == (KIMAGE_VADDR + TEXT_OFFSET), "HEAD is misaligned")