diff options
Diffstat (limited to 'arch/arm64/kernel/vdso')
| -rw-r--r-- | arch/arm64/kernel/vdso/Makefile | 12 | ||||
| -rw-r--r-- | arch/arm64/kernel/vdso/note.S | 3 | ||||
| -rw-r--r-- | arch/arm64/kernel/vdso/sigreturn.S | 54 | ||||
| -rw-r--r-- | arch/arm64/kernel/vdso/vdso.S | 3 |
4 files changed, 61 insertions, 11 deletions
diff --git a/arch/arm64/kernel/vdso/Makefile b/arch/arm64/kernel/vdso/Makefile index 3862cad2410c..556d424c6f52 100644 --- a/arch/arm64/kernel/vdso/Makefile +++ b/arch/arm64/kernel/vdso/Makefile @@ -17,15 +17,19 @@ obj-vdso := vgettimeofday.o note.o sigreturn.o targets := $(obj-vdso) vdso.so vdso.so.dbg obj-vdso := $(addprefix $(obj)/, $(obj-vdso)) +btildflags-$(CONFIG_ARM64_BTI_KERNEL) += -z force-bti + +# -Bsymbolic has been added for consistency with arm, the compat vDSO and +# potential future proofing if we end up with internal calls to the exported +# routines, as x86 does (see 6f121e548f83 ("x86, vdso: Reimplement vdso.so +# preparation in build-time C")). ldflags-y := -shared -nostdlib -soname=linux-vdso.so.1 --hash-style=sysv \ - --build-id -n -T + -Bsymbolic --eh-frame-hdr --build-id -n $(btildflags-y) -T ccflags-y := -fno-common -fno-builtin -fno-stack-protector -ffixed-x18 ccflags-y += -DDISABLE_BRANCH_PROFILING -VDSO_LDFLAGS := -Bsymbolic - -CFLAGS_REMOVE_vgettimeofday.o = $(CC_FLAGS_FTRACE) -Os +CFLAGS_REMOVE_vgettimeofday.o = $(CC_FLAGS_FTRACE) -Os $(CC_FLAGS_SCS) KBUILD_CFLAGS += $(DISABLE_LTO) KASAN_SANITIZE := n UBSAN_SANITIZE := n diff --git a/arch/arm64/kernel/vdso/note.S b/arch/arm64/kernel/vdso/note.S index 0ce6ec75a525..3d4e82290c80 100644 --- a/arch/arm64/kernel/vdso/note.S +++ b/arch/arm64/kernel/vdso/note.S @@ -12,9 +12,12 @@ #include <linux/version.h> #include <linux/elfnote.h> #include <linux/build-salt.h> +#include <asm/assembler.h> ELFNOTE_START(Linux, 0, "a") .long LINUX_VERSION_CODE ELFNOTE_END BUILD_SALT + +emit_aarch64_feature_1_and diff --git a/arch/arm64/kernel/vdso/sigreturn.S b/arch/arm64/kernel/vdso/sigreturn.S index 12324863d5c2..620a3ef837b7 100644 --- a/arch/arm64/kernel/vdso/sigreturn.S +++ b/arch/arm64/kernel/vdso/sigreturn.S @@ -1,7 +1,11 @@ /* SPDX-License-Identifier: GPL-2.0-only */ /* * Sigreturn trampoline for returning from a signal when the SA_RESTORER - * flag is not set. + * flag is not set. It serves primarily as a hall of shame for crappy + * unwinders and features an exciting but mysterious NOP instruction. + * + * It's also fragile as hell, so please think twice before changing anything + * in here. * * Copyright (C) 2012 ARM Limited * @@ -9,18 +13,54 @@ */ #include <linux/linkage.h> +#include <asm/assembler.h> #include <asm/unistd.h> .text - nop -SYM_FUNC_START(__kernel_rt_sigreturn) +/* Ensure that the mysterious NOP can be associated with a function. */ .cfi_startproc + +/* + * .cfi_signal_frame causes the corresponding Frame Description Entry in the + * .eh_frame section to be annotated as a signal frame. This allows DWARF + * unwinders (e.g. libstdc++) to implement _Unwind_GetIPInfo(), which permits + * unwinding out of the signal trampoline without the need for the mysterious + * NOP. + */ .cfi_signal_frame - .cfi_def_cfa x29, 0 - .cfi_offset x29, 0 * 8 - .cfi_offset x30, 1 * 8 + +/* + * Tell the unwinder where to locate the frame record linking back to the + * interrupted context. We don't provide unwind info for registers other + * than the frame pointer and the link register here; in practice, this + * is sufficient for unwinding in C/C++ based runtimes and the values in + * the sigcontext may have been modified by this point anyway. Debuggers + * already have baked-in strategies for attempting to unwind out of signals. + */ + .cfi_def_cfa x29, 0 + .cfi_offset x29, 0 * 8 + .cfi_offset x30, 1 * 8 + +/* + * This mysterious NOP is required for some unwinders (e.g. libc++) that + * unconditionally subtract one from the result of _Unwind_GetIP() in order to + * identify the calling function. + * Hack borrowed from arch/powerpc/kernel/vdso64/sigtramp.S. + */ + nop // Mysterious NOP + +/* + * GDB relies on being able to identify the sigreturn instruction sequence to + * unwind from signal handlers. We cannot, therefore, use SYM_FUNC_START() + * here, as it will emit a BTI C instruction and break the unwinder. Thankfully, + * this function is only ever called from a RET and so omitting the landing pad + * is perfectly fine. + */ +SYM_CODE_START(__kernel_rt_sigreturn) mov x8, #__NR_rt_sigreturn svc #0 .cfi_endproc -SYM_FUNC_END(__kernel_rt_sigreturn) +SYM_CODE_END(__kernel_rt_sigreturn) + +emit_aarch64_feature_1_and diff --git a/arch/arm64/kernel/vdso/vdso.S b/arch/arm64/kernel/vdso/vdso.S index d1414fee5274..c4b1990bf2be 100644 --- a/arch/arm64/kernel/vdso/vdso.S +++ b/arch/arm64/kernel/vdso/vdso.S @@ -8,6 +8,7 @@ #include <linux/init.h> #include <linux/linkage.h> #include <linux/const.h> +#include <asm/assembler.h> #include <asm/page.h> .globl vdso_start, vdso_end @@ -19,3 +20,5 @@ vdso_start: vdso_end: .previous + +emit_aarch64_feature_1_and |