Le 16/05/2022 à 09:32, Xiu Jianfeng a écrit : > 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 <xiujianf...@huawei.com> >
Did you see this patch generates sparse warnings ? See https://patchwork.ozlabs.org/project/linuxppc-dev/patch/20220516073225.112875-1-xiujianf...@huawei.com/ It is not directly related to this patch but that's worth a patch to fix it. > --- > 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)
