[PATCH v3 5/6] arm64: module: mandate MODULE_PLTS
Mark Rutland
mark.rutland at arm.com
Tue May 30 04:03:27 PDT 2023
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 at arm.com>
Reviewed-by: Ard Biesheuvel <ardb at kernel.org>
Cc: Catalin Marinas <catalin.marinas at arm.com>
Cc: Shanker Donthineni <sdonthineni at nvidia.com>
Cc: Will Deacon <will at kernel.org>
---
arch/arm64/Kconfig | 28 +++-------------------------
arch/arm64/include/asm/module.h | 2 --
arch/arm64/include/asm/module.lds.h | 2 --
arch/arm64/kernel/Makefile | 3 +--
arch/arm64/kernel/ftrace.c | 8 +++-----
arch/arm64/kernel/module.c | 25 ++++++++++++-------------
6 files changed, 19 insertions(+), 49 deletions(-)
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index b1201d25a8a4..a6002084f09c 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -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 $(cc-option,-mstack-protector-guard=sysreg -mstack-protector-guard-reg=sp_el0 -mstack-protector-guard-offset=0)
diff --git a/arch/arm64/include/asm/module.h b/arch/arm64/include/asm/module.h
index 3e7dcc5fa2f2..bfa6638b4c93 100644
--- a/arch/arm64/include/asm/module.h
+++ b/arch/arm64/include/asm/module.h
@@ -7,7 +7,6 @@
#include <asm-generic/module.h>
-#ifdef CONFIG_ARM64_MODULE_PLTS
struct mod_plt_sec {
int plt_shndx;
int plt_num_entries;
@@ -21,7 +20,6 @@ struct mod_arch_specific {
/* for CONFIG_DYNAMIC_FTRACE */
struct plt_entry *ftrace_trampolines;
};
-#endif
u64 module_emit_plt_entry(struct module *mod, Elf64_Shdr *sechdrs,
void *loc, const Elf64_Rela *rela,
diff --git a/arch/arm64/include/asm/module.lds.h b/arch/arm64/include/asm/module.lds.h
index dbba4b7559aa..b9ae8349e35d 100644
--- a/arch/arm64/include/asm/module.lds.h
+++ b/arch/arm64/include/asm/module.lds.h
@@ -1,9 +1,7 @@
SECTIONS {
-#ifdef CONFIG_ARM64_MODULE_PLTS
.plt 0 : { BYTE(0) }
.init.plt 0 : { BYTE(0) }
.text.ftrace_trampoline 0 : { BYTE(0) }
-#endif
#ifdef CONFIG_KASAN_SW_TAGS
/*
diff --git a/arch/arm64/kernel/Makefile b/arch/arm64/kernel/Makefile
index 7c2bb4e72476..3864a64e2b2b 100644
--- a/arch/arm64/kernel/Makefile
+++ b/arch/arm64/kernel/Makefile
@@ -42,8 +42,7 @@ obj-$(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
diff --git a/arch/arm64/kernel/ftrace.c b/arch/arm64/kernel/ftrace.c
index 432626c866a8..a650f5e11fc5 100644
--- a/arch/arm64/kernel/ftrace.c
+++ b/arch/arm64/kernel/ftrace.c
@@ -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;
diff --git a/arch/arm64/kernel/module.c b/arch/arm64/kernel/module.c
index 51fd8abd9b74..f64636c2fd05 100644
--- a/arch/arm64/kernel/module.c
+++ b/arch/arm64/kernel/module.c
@@ -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;
--
2.30.2
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