@@ -195,6 +195,7 @@ config PPC
select HAVE_ARCH_KASAN if PPC_RADIX_MMU
select HAVE_ARCH_KASAN_VMALLOC if HAVE_ARCH_KASAN
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
@@ -53,6 +53,13 @@ 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_syscall.o = -fstack-protector -fstack-protector-strong
+CFLAGS_syscall.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 \
@@ -2,6 +2,7 @@
#include <linux/compat.h>
#include <linux/context_tracking.h>
+#include <linux/randomize_kstack.h>
#include <asm/interrupt.h>
#include <asm/kup.h>
@@ -18,10 +19,12 @@ 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))
@@ -169,5 +172,19 @@ 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;
}
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> --- arch/powerpc/Kconfig | 1 + arch/powerpc/kernel/Makefile | 7 +++++++ arch/powerpc/kernel/syscall.c | 19 ++++++++++++++++++- 3 files changed, 26 insertions(+), 1 deletion(-)