Messages in this thread | | | Subject | Re: [PATCH -next, v2] powerpc: add support for syscall stack randomization | From | xiujianfeng <> | Date | Thu, 16 Jun 2022 09:51:03 +0800 |
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在 2022/5/28 20:21, Michael Ellerman 写道: > xiujianfeng <xiujianfeng@huawei.com> writes: >> friendly ping.... > I will consider this for v5.20 once the merge window has closed (after > v5.19-rc1 is release).
Hi, Michael, thanks for your feedback, and anything needed about this patch please let me know :)
> > cheers > >> 在 2022/5/16 15:32, Xiu Jianfeng 写道: >>> Add support for adding a random offset to the stack while handling >>> syscalls. This patch uses mftb() instead of get_random_int() for better >>> performance. >>> >>> In order to avoid unconditional stack canaries on syscall entry (due to >>> the use of alloca()), also disable stack protector to avoid triggering >>> needless checks and slowing down the entry path. As there is no general >>> way to control stack protector coverage with a function attribute, this >>> must be disabled at the compilation unit level. >>> >>> Signed-off-by: Xiu Jianfeng <xiujianfeng@huawei.com> >>> >>> --- >>> Changes in v2: >>> -move choose choose_random_kstack_offset() to the end of system_call_exception >>> -allow full 6 (10) bits of entropy >>> -disable stack-protector for interrupt.c >>> --- >>> arch/powerpc/Kconfig | 1 + >>> arch/powerpc/kernel/Makefile | 7 +++++++ >>> arch/powerpc/kernel/interrupt.c | 19 ++++++++++++++++++- >>> 3 files changed, 26 insertions(+), 1 deletion(-) >>> >>> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig >>> index 98309eeae09c..2f0019a0054e 100644 >>> --- a/arch/powerpc/Kconfig >>> +++ b/arch/powerpc/Kconfig >>> @@ -192,6 +192,7 @@ config PPC >>> select HAVE_ARCH_KASAN if PPC32 && PPC_PAGE_SHIFT <= 14 >>> select HAVE_ARCH_KASAN_VMALLOC if PPC32 && PPC_PAGE_SHIFT <= 14 >>> select HAVE_ARCH_KFENCE if PPC_BOOK3S_32 || PPC_8xx || 40x >>> + select HAVE_ARCH_RANDOMIZE_KSTACK_OFFSET >>> select HAVE_ARCH_KGDB >>> select HAVE_ARCH_MMAP_RND_BITS >>> select HAVE_ARCH_MMAP_RND_COMPAT_BITS if COMPAT >>> diff --git a/arch/powerpc/kernel/Makefile b/arch/powerpc/kernel/Makefile >>> index 4ddd161aef32..5c5e85b8229b 100644 >>> --- a/arch/powerpc/kernel/Makefile >>> +++ b/arch/powerpc/kernel/Makefile >>> @@ -40,6 +40,13 @@ CFLAGS_cputable.o += -DDISABLE_BRANCH_PROFILING >>> CFLAGS_btext.o += -DDISABLE_BRANCH_PROFILING >>> endif >>> >>> +#ifdef CONFIG_RANDOMIZE_KSTACK_OFFSET >>> +# Remove stack protector to avoid triggering unneeded stack canary >>> +# checks due to randomize_kstack_offset. >>> +CFLAGS_REMOVE_interrupt.o = -fstack-protector -fstack-protector-strong >>> +CFLAGS_interrupt.o += -fno-stack-protector >>> +#endif >>> + >>> obj-y := cputable.o syscalls.o \ >>> irq.o align.o signal_$(BITS).o pmc.o vdso.o \ >>> process.o systbl.o idle.o \ >>> diff --git a/arch/powerpc/kernel/interrupt.c b/arch/powerpc/kernel/interrupt.c >>> index 784ea3289c84..d7cdcb6fc336 100644 >>> --- a/arch/powerpc/kernel/interrupt.c >>> +++ b/arch/powerpc/kernel/interrupt.c >>> @@ -4,6 +4,7 @@ >>> #include <linux/err.h> >>> #include <linux/compat.h> >>> #include <linux/sched/debug.h> /* for show_regs */ >>> +#include <linux/randomize_kstack.h> >>> >>> #include <asm/kup.h> >>> #include <asm/cputime.h> >>> @@ -78,10 +79,12 @@ notrace long system_call_exception(long r3, long r4, long r5, >>> long r6, long r7, long r8, >>> unsigned long r0, struct pt_regs *regs) >>> { >>> + long ret; >>> syscall_fn f; >>> >>> kuap_lock(); >>> >>> + add_random_kstack_offset(); >>> regs->orig_gpr3 = r3; >>> >>> if (IS_ENABLED(CONFIG_PPC_IRQ_SOFT_MASK_DEBUG)) >>> @@ -229,7 +232,21 @@ notrace long system_call_exception(long r3, long r4, long r5, >>> f = (void *)sys_call_table[r0]; >>> } >>> >>> - return f(r3, r4, r5, r6, r7, r8); >>> + ret = f(r3, r4, r5, r6, r7, r8); >>> + /* >>> + * Ultimately, this value will get limited by KSTACK_OFFSET_MAX(), >>> + * so the maximum stack offset is 1k bytes(10 bits). >>> + * >>> + * The actual entropy will be further reduced by the compiler when >>> + * applying stack alignment constraints: the powerpc architecture >>> + * may have two kinds of stack alignment(16-bytes and 8-bytes). >>> + * >>> + * So the resulting 6 or 7 bits of entropy is seen in SP[9:4] or SP[9:3]. >>> + * >>> + */ >>> + choose_random_kstack_offset(mftb()); >>> + >>> + return ret; >>> } >>> >>> static notrace void booke_load_dbcr0(void) > .
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