xiujianfeng <xiujianf...@huawei.com> writes:
> friendly ping....
I will consider this for v5.20 once the merge window has closed (after
v5.19-rc1 is release).
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 <xiujianf...@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)
