| Message ID | 20240925150059.3955569-35-ardb+git@google.com |
|---|---|
| State | New |
| Headers | show |
| Series | x86: Rely on toolchain for relocatable code | expand |
On Wed, Sep 25, 2024 at 5:02 PM Ard Biesheuvel <ardb+git@google.com> wrote: > > From: Ard Biesheuvel <ardb@kernel.org> > > Specify the guard symbol for the stack cookie explicitly, rather than > positioning it exactly 40 bytes into the per-CPU area. Doing so removes > the need for the per-CPU region to be absolute rather than relative to > the placement of the per-CPU template region in the kernel image, and > this allows the special handling for absolute per-CPU symbols to be > removed entirely. > > This is a worthwhile cleanup in itself, but it is also a prerequisite > for PIE codegen and PIE linking, which can replace our bespoke and > rather clunky runtime relocation handling. > > Signed-off-by: Ard Biesheuvel <ardb@kernel.org> > --- > arch/x86/Makefile | 4 ++++ > arch/x86/include/asm/init.h | 2 +- > arch/x86/include/asm/processor.h | 11 +++-------- > arch/x86/include/asm/stackprotector.h | 4 ---- > tools/perf/util/annotate.c | 4 ++-- > 5 files changed, 10 insertions(+), 15 deletions(-) > > diff --git a/arch/x86/Makefile b/arch/x86/Makefile > index 6b3fe6e2aadd..b78b7623a4a9 100644 > --- a/arch/x86/Makefile > +++ b/arch/x86/Makefile > @@ -193,6 +193,10 @@ else > KBUILD_RUSTFLAGS += -Cno-redzone=y > KBUILD_RUSTFLAGS += -Ccode-model=kernel > > + ifeq ($(CONFIG_STACKPROTECTOR),y) > + KBUILD_CFLAGS += -mstack-protector-guard-symbol=fixed_percpu_data Looking at: > + * Since the irq_stack is the object at %gs:0, the bottom 8 bytes of > + * the irq stack are reserved for the canary. Please note that %gs:0 can also be achieved with -mstack-protector-guard-offset=0 Uros.
diff --git a/arch/x86/Makefile b/arch/x86/Makefile index 6b3fe6e2aadd..b78b7623a4a9 100644 --- a/arch/x86/Makefile +++ b/arch/x86/Makefile @@ -193,6 +193,10 @@ else KBUILD_RUSTFLAGS += -Cno-redzone=y KBUILD_RUSTFLAGS += -Ccode-model=kernel + ifeq ($(CONFIG_STACKPROTECTOR),y) + KBUILD_CFLAGS += -mstack-protector-guard-symbol=fixed_percpu_data + endif + # Don't emit relaxable GOTPCREL relocations KBUILD_AFLAGS_KERNEL += -Wa,-mrelax-relocations=no KBUILD_CFLAGS_KERNEL += -Wa,-mrelax-relocations=no diff --git a/arch/x86/include/asm/init.h b/arch/x86/include/asm/init.h index 14d72727d7ee..3ed0e8ec973f 100644 --- a/arch/x86/include/asm/init.h +++ b/arch/x86/include/asm/init.h @@ -2,7 +2,7 @@ #ifndef _ASM_X86_INIT_H #define _ASM_X86_INIT_H -#define __head __section(".head.text") +#define __head __section(".head.text") __no_stack_protector struct x86_mapping_info { void *(*alloc_pgt_page)(void *); /* allocate buf for page table */ diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h index 4a686f0e5dbf..56bc36116814 100644 --- a/arch/x86/include/asm/processor.h +++ b/arch/x86/include/asm/processor.h @@ -402,14 +402,9 @@ struct irq_stack { #ifdef CONFIG_X86_64 struct fixed_percpu_data { /* - * GCC hardcodes the stack canary as %gs:40. Since the - * irq_stack is the object at %gs:0, we reserve the bottom - * 48 bytes of the irq stack for the canary. - * - * Once we are willing to require -mstack-protector-guard-symbol= - * support for x86_64 stackprotector, we can get rid of this. + * Since the irq_stack is the object at %gs:0, the bottom 8 bytes of + * the irq stack are reserved for the canary. */ - char gs_base[40]; unsigned long stack_canary; }; @@ -418,7 +413,7 @@ DECLARE_INIT_PER_CPU(fixed_percpu_data); static inline unsigned long cpu_kernelmode_gs_base(int cpu) { - return (unsigned long)per_cpu(fixed_percpu_data.gs_base, cpu); + return (unsigned long)&per_cpu(fixed_percpu_data, cpu); } extern asmlinkage void entry_SYSCALL32_ignore(void); diff --git a/arch/x86/include/asm/stackprotector.h b/arch/x86/include/asm/stackprotector.h index 00473a650f51..d1dcd22a0a4c 100644 --- a/arch/x86/include/asm/stackprotector.h +++ b/arch/x86/include/asm/stackprotector.h @@ -51,10 +51,6 @@ static __always_inline void boot_init_stack_canary(void) { unsigned long canary = get_random_canary(); -#ifdef CONFIG_X86_64 - BUILD_BUG_ON(offsetof(struct fixed_percpu_data, stack_canary) != 40); -#endif - current->stack_canary = canary; #ifdef CONFIG_X86_64 this_cpu_write(fixed_percpu_data.stack_canary, canary); diff --git a/tools/perf/util/annotate.c b/tools/perf/util/annotate.c index 37ce43c4eb8f..7ecfedf5edb9 100644 --- a/tools/perf/util/annotate.c +++ b/tools/perf/util/annotate.c @@ -2485,10 +2485,10 @@ static bool is_stack_operation(struct arch *arch, struct disasm_line *dl) static bool is_stack_canary(struct arch *arch, struct annotated_op_loc *loc) { - /* On x86_64, %gs:40 is used for stack canary */ + /* On x86_64, %gs:0 is used for stack canary */ if (arch__is(arch, "x86")) { if (loc->segment == INSN_SEG_X86_GS && loc->imm && - loc->offset == 40) + loc->offset == 0) return true; }