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arm64: module: mandate MODULE_PLTS

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Contemporary kernels and modules can be relatively large, especially
when common debug options are enabled. Using GCC 12.1.0, a v6.3-rc7
defconfig kernel is ~38M, and with PROVE_LOCKING + KASAN_INLINE enabled
this expands to ~117M. Shanker reports [1] that the NVIDIA GPU driver
alone can consume 110M of module space in some configurations.

Both KASLR and ARM64_ERRATUM_843419 select MODULE_PLTS, so anyone
wanting a kernel to have KASLR or run on Cortex-A53 will have
MODULE_PLTS selected. This is the case in defconfig and distribution
kernels (e.g. Debian, Android, etc).

Practically speaking, this means we're very likely to need MODULE_PLTS
and while it's almost guaranteed that MODULE_PLTS will be selected, it
is possible to disable support, and we have to maintain some awkward
special cases for such unusual configurations.

This patch removes the MODULE_PLTS config option, with the support code
always enabled if MODULES is selected. This results in a slight
simplification, and will allow for further improvement in subsequent
patches.

For any config which currently selects MODULE_PLTS, there will be no
functional change as a result of this patch.

[1] https://lore.kernel.org/linux-arm-kernel/159ceeab-09af-3174-5058-445bc8dcf85b@nvidia.com/

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Ard Biesheuvel <ardb@kernel.org>
Cc: Shanker Donthineni <sdonthineni@nvidia.com>
Cc: Will Deacon <will@kernel.org>
Tested-by: Shanker Donthineni <sdonthineni@nvidia.com>
Link: https://lore.kernel.org/r/20230530110328.2213762-6-mark.rutland@arm.com
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
This commit is contained in:
Mark Rutland 2023-05-30 12:03:27 +01:00 committed by Catalin Marinas
parent e46b7103ae
commit ea3752ba96
6 changed files with 19 additions and 49 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

28
arch/arm64/Kconfig
View File

@ -207,6 +207,7 @@ config ARM64
select HAVE_IOREMAP_PROT
select HAVE_IRQ_TIME_ACCOUNTING
select HAVE_KVM
select HAVE_MOD_ARCH_SPECIFIC
select HAVE_NMI
select HAVE_PERF_EVENTS
select HAVE_PERF_REGS
@ -577,7 +578,6 @@ config ARM64_ERRATUM_845719
config ARM64_ERRATUM_843419
bool "Cortex-A53: 843419: A load or store might access an incorrect address"
default y
select ARM64_MODULE_PLTS if MODULES
help
This option links the kernel with '--fix-cortex-a53-843419' and
enables PLT support to replace certain ADRP instructions, which can
@ -2107,26 +2107,6 @@ config ARM64_SME
register state capable of holding two dimensional matrix tiles to
enable various matrix operations.
config ARM64_MODULE_PLTS
bool "Use PLTs to allow module memory to spill over into vmalloc area"
depends on MODULES
select HAVE_MOD_ARCH_SPECIFIC
help
Allocate PLTs when loading modules so that jumps and calls whose
targets are too far away for their relative offsets to be encoded
in the instructions themselves can be bounced via veneers in the
module's PLT. This allows modules to be allocated in the generic
vmalloc area after the dedicated module memory area has been
exhausted.
When running with address space randomization (KASLR), the module
region itself may be too far away for ordinary relative jumps and
calls, and so in that case, module PLTs are required and cannot be
disabled.
Specific errata workaround(s) might also force module PLTs to be
enabled (ARM64_ERRATUM_843419).
config ARM64_PSEUDO_NMI
bool "Support for NMI-like interrupts"
select ARM_GIC_V3
@ -2167,7 +2147,6 @@ config RELOCATABLE
config RANDOMIZE_BASE
bool "Randomize the address of the kernel image"
select ARM64_MODULE_PLTS if MODULES
select RELOCATABLE
help
Randomizes the virtual address at which the kernel image is
@ -2198,9 +2177,8 @@ config RANDOMIZE_MODULE_REGION_FULL
When this option is not set, the module region will be randomized over
a limited range that contains the [_stext, _etext] interval of the
core kernel, so branch relocations are almost always in range unless
ARM64_MODULE_PLTS is enabled and the region is exhausted. In this
particular case of region exhaustion, modules might be able to fall
back to a larger 2GB area.
the region is exhausted. In this particular case of region
exhaustion, modules might be able to fall back to a larger 2GB area.
config CC_HAVE_STACKPROTECTOR_SYSREG
def_bool $(cc-option,-mstack-protector-guard=sysreg -mstack-protector-guard-reg=sp_el0 -mstack-protector-guard-offset=0)

2
arch/arm64/include/asm/module.h
View File

@ -7,7 +7,6 @@
#include <asm-generic/module.h>
#ifdef CONFIG_ARM64_MODULE_PLTS
struct mod_plt_sec {
int plt_shndx;
int plt_num_entries;
@ -21,7 +20,6 @@ struct mod_arch_specific {
/* for CONFIG_DYNAMIC_FTRACE */
struct plt_entry *ftrace_trampolines;
};
#endif
u64 module_emit_plt_entry(struct module *mod, Elf64_Shdr *sechdrs,
void *loc, const Elf64_Rela *rela,

2
arch/arm64/include/asm/module.lds.h
View File

@ -1,9 +1,7 @@
SECTIONS {
#ifdef CONFIG_ARM64_MODULE_PLTS
.plt 0 : { BYTE(0) }
.init.plt 0 : { BYTE(0) }
.text.ftrace_trampoline 0 : { BYTE(0) }
#endif
#ifdef CONFIG_KASAN_SW_TAGS
/*

3
arch/arm64/kernel/Makefile
View File

@ -42,8 +42,7 @@ obj-$(CONFIG_COMPAT) += sigreturn32.o
obj-$(CONFIG_COMPAT_ALIGNMENT_FIXUPS) += compat_alignment.o
obj-$(CONFIG_KUSER_HELPERS) += kuser32.o
obj-$(CONFIG_FUNCTION_TRACER) += ftrace.o entry-ftrace.o
obj-$(CONFIG_MODULES) += module.o
obj-$(CONFIG_ARM64_MODULE_PLTS) += module-plts.o
obj-$(CONFIG_MODULES) += module.o module-plts.o
obj-$(CONFIG_PERF_EVENTS) += perf_regs.o perf_callchain.o
obj-$(CONFIG_HAVE_HW_BREAKPOINT) += hw_breakpoint.o
obj-$(CONFIG_CPU_PM) += sleep.o suspend.o

8
arch/arm64/kernel/ftrace.c
View File

@ -197,7 +197,7 @@ int ftrace_update_ftrace_func(ftrace_func_t func)
static struct plt_entry *get_ftrace_plt(struct module *mod)
{
#ifdef CONFIG_ARM64_MODULE_PLTS
#ifdef CONFIG_MODULES
struct plt_entry *plt = mod->arch.ftrace_trampolines;
return &plt[FTRACE_PLT_IDX];
@ -249,7 +249,7 @@ static bool ftrace_find_callable_addr(struct dyn_ftrace *rec,
* must use a PLT to reach it. We can only place PLTs for modules, and
* only when module PLT support is built-in.
*/
if (!IS_ENABLED(CONFIG_ARM64_MODULE_PLTS))
if (!IS_ENABLED(CONFIG_MODULES))
return false;
/*
@ -431,10 +431,8 @@ int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec,
*
* Note: 'mod' is only set at module load time.
*/
if (!IS_ENABLED(CONFIG_DYNAMIC_FTRACE_WITH_ARGS) &&
IS_ENABLED(CONFIG_ARM64_MODULE_PLTS) && mod) {
if (!IS_ENABLED(CONFIG_DYNAMIC_FTRACE_WITH_ARGS) && mod)
return aarch64_insn_patch_text_nosync((void *)pc, new);
}
if (!ftrace_find_callable_addr(rec, mod, &addr))
return -EINVAL;

25
arch/arm64/kernel/module.c
View File

@ -73,25 +73,26 @@ subsys_initcall(kaslr_module_init)
void *module_alloc(unsigned long size)
{
u64 module_alloc_end = module_alloc_base + MODULES_VSIZE;
gfp_t gfp_mask = GFP_KERNEL;
void *p;
/* Silence the initial allocation */
if (IS_ENABLED(CONFIG_ARM64_MODULE_PLTS))
gfp_mask |= __GFP_NOWARN;
/*
* Where possible, prefer to allocate within direct branch range of the
* kernel such that no PLTs are necessary. This may fail, so we pass
* __GFP_NOWARN to silence the resulting warning.
*/
p = __vmalloc_node_range(size, MODULE_ALIGN, module_alloc_base,
module_alloc_end, gfp_mask, PAGE_KERNEL, 0,
NUMA_NO_NODE, __builtin_return_address(0));
module_alloc_end, GFP_KERNEL | __GFP_NOWARN,
PAGE_KERNEL, 0, NUMA_NO_NODE,
__builtin_return_address(0));
if (!p && IS_ENABLED(CONFIG_ARM64_MODULE_PLTS)) {
if (!p) {
p = __vmalloc_node_range(size, MODULE_ALIGN, module_alloc_base,
module_alloc_base + SZ_2G, GFP_KERNEL,
PAGE_KERNEL, 0, NUMA_NO_NODE,
__builtin_return_address(0));
}
if (p && (kasan_alloc_module_shadow(p, size, gfp_mask) < 0)) {
if (p && (kasan_alloc_module_shadow(p, size, GFP_KERNEL) < 0)) {
vfree(p);
return NULL;
}
@ -479,9 +480,7 @@ int apply_relocate_add(Elf64_Shdr *sechdrs,
case R_AARCH64_CALL26:
ovf = reloc_insn_imm(RELOC_OP_PREL, loc, val, 2, 26,
AARCH64_INSN_IMM_26);
if (IS_ENABLED(CONFIG_ARM64_MODULE_PLTS) &&
ovf == -ERANGE) {
if (ovf == -ERANGE) {
val = module_emit_plt_entry(me, sechdrs, loc, &rel[i], sym);
if (!val)
return -ENOEXEC;
@ -518,7 +517,7 @@ static int module_init_ftrace_plt(const Elf_Ehdr *hdr,
const Elf_Shdr *sechdrs,
struct module *mod)
{
#if defined(CONFIG_ARM64_MODULE_PLTS) && defined(CONFIG_DYNAMIC_FTRACE)
#if defined(CONFIG_DYNAMIC_FTRACE)
const Elf_Shdr *s;
struct plt_entry *plts;