Re: [PATCH V6 09/11] riscv: Add support for STACKLEAK gcc plugin

[Guo Ren <guoren@kernel.org>]

Hi Mark,

Here is the test result with stackleak_erase_on_task_stack.

# echo STACKLEAK_ERASING > /sys/kernel/debug/provoke-crash/DIRECT
[   53.110405] lkdtm: Performing direct entry STACKLEAK_ERASING
[   53.111630] lkdtm: stackleak stack usage:
[   53.111630]   high offset: 288 bytes
[   53.111630]   current:     592 bytes
[   53.111630]   lowest:      1136 bytes
[   53.111630]   tracked:     1136 bytes
[   53.111630]   untracked:   576 bytes
[   53.111630]   poisoned:    14376 bytes
[   53.111630]   low offset:  8 bytes
[   53.115078] lkdtm: OK: the rest of the thread stack is properly erased

On Sat, Oct 8, 2022 at 11:26 AM Guo Ren <guoren@kernel.org> wrote:
>
> On Mon, Oct 3, 2022 at 7:34 PM Mark Rutland <mark.rutland@arm.com> wrote:
> >
> > On Sat, Oct 01, 2022 at 09:24:49PM -0400, guoren@kernel.org wrote:
> > > From: Dao Lu <daolu@rivosinc.com>
> > >
> > > Add support for STACKLEAK gcc plugin to riscv by implementing
> > > stackleak_check_alloca, based heavily on the arm64 version, and
> > > modifying the entry.S. Additionally, this disables the plugin for EFI
> > > stub code for riscv. All modifications base on generic_entry.
> >
> > I think this commit message is stale; `stackleak_check_alloca` doesn't exist
> > any more.
> >
> > > Link: https://lore.kernel.org/linux-riscv/20220615213834.3116135-1-daolu@rivosinc.com/
> > > Signed-off-by: Dao Lu <daolu@rivosinc.com>
> > > Co-developed-by: Xianting Tian <xianting.tian@linux.alibaba.com>
> > > Signed-off-by: Xianting Tian <xianting.tian@linux.alibaba.com>
> > > Co-developed-by: Guo Ren <guoren@kernel.org>
> > > Signed-off-by: Guo Ren <guoren@kernel.org>
> > > Cc: Conor Dooley <Conor.Dooley@microchip.com>
> > > Cc: Mark Rutland <mark.rutland@arm.com>
> > > ---
> > >  arch/riscv/Kconfig                    | 1 +
> > >  arch/riscv/kernel/entry.S             | 8 +++++++-
> > >  drivers/firmware/efi/libstub/Makefile | 2 +-
> > >  3 files changed, 9 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> > > index dfe600f3526c..76bde12d9f8c 100644
> > > --- a/arch/riscv/Kconfig
> > > +++ b/arch/riscv/Kconfig
> > > @@ -81,6 +81,7 @@ config RISCV
> > >       select HAVE_ARCH_MMAP_RND_BITS if MMU
> > >       select HAVE_ARCH_MMAP_RND_COMPAT_BITS if COMPAT
> > >       select HAVE_ARCH_SECCOMP_FILTER
> > > +     select HAVE_ARCH_STACKLEAK
> > >       select HAVE_ARCH_TRACEHOOK
> > >       select HAVE_ARCH_TRANSPARENT_HUGEPAGE if 64BIT && MMU
> > >       select ARCH_ENABLE_THP_MIGRATION if TRANSPARENT_HUGEPAGE
> > > diff --git a/arch/riscv/kernel/entry.S b/arch/riscv/kernel/entry.S
> > > index 5f49517cd3a2..39097c1474a0 100644
> > > --- a/arch/riscv/kernel/entry.S
> > > +++ b/arch/riscv/kernel/entry.S
> > > @@ -130,7 +130,6 @@ END(handle_exception)
> > >  ENTRY(ret_from_exception)
> > >       REG_L s0, PT_STATUS(sp)
> > >
> > > -     csrc CSR_STATUS, SR_IE
> > >  #ifdef CONFIG_RISCV_M_MODE
> > >       /* the MPP value is too large to be used as an immediate arg for addi */
> > >       li t0, SR_MPP
> > > @@ -139,6 +138,9 @@ ENTRY(ret_from_exception)
> > >       andi s0, s0, SR_SPP
> > >  #endif
> > >       bnez s0, 1f
> > > +#ifdef CONFIG_GCC_PLUGIN_STACKLEAK
> > > +     call stackleak_erase
> > > +#endif
> >
> > I assume this can happen on an arbitrary stack, and so you can't use the
> > stackleak_erase_{on,off}_task_stack variants?
> I misunderstood before.
>
> Yes, riscv could use stackleak_erase_on_task_stack. Because the sp has
> changed to task_stack, even when irq/soft_irq.
>
> >
> > Just to check, have you given this a spin with LKDTM and the STACKLEAK_ERASING
> > test? If not, it'd be good to test that (and ideally, put some sample output
> > from that into the commit message).
> >
> > For example, as per:
> >
> >   https://lore.kernel.org/all/20220427173128.2603085-1-mark.rutland@arm.com/
> >
> > ... on arm64 this looks something like:
> >
> > | # uname -a
> > | Linux buildroot 5.18.0-rc1-00013-g26f638ab0d7c #3 SMP PREEMPT Wed Apr 27 16:21:37 BST 2022 aarch64 GNU/Linux
> > | # echo STACKLEAK_ERASING > /sys/kernel/debug/provoke-crash/DIRECT
> > | lkdtm: Performing direct entry STACKLEAK_ERASING
> > | lkdtm: stackleak stack usage:
> > |   high offset: 336 bytes
> > |   current:     688 bytes
> > |   lowest:      1232 bytes
> > |   tracked:     1232 bytes
> > |   untracked:   672 bytes
> > |   poisoned:    14136 bytes
> > |   low offset:  8 bytes
> > | lkdtm: OK: the rest of the thread stack is properly erased
> >
> > Thanks,
> > Mark.
> >
> > >
> > >       /* Save unwound kernel stack pointer in thread_info */
> > >       addi s0, sp, PT_SIZE_ON_STACK
> > > @@ -148,8 +150,12 @@ ENTRY(ret_from_exception)
> > >        * Save TP into the scratch register , so we can find the kernel data
> > >        * structures again.
> > >        */
> > > +     csrc CSR_STATUS, SR_IE
> > >       csrw CSR_SCRATCH, tp
> > > +     j 2f
> > >  1:
> > > +     csrc CSR_STATUS, SR_IE
> > > +2:
> > >       /*
> > >        * The current load reservation is effectively part of the processor's
> > >        * state, in the sense that load reservations cannot be shared between
> > > diff --git a/drivers/firmware/efi/libstub/Makefile b/drivers/firmware/efi/libstub/Makefile
> > > index d0537573501e..5e1fc4f82883 100644
> > > --- a/drivers/firmware/efi/libstub/Makefile
> > > +++ b/drivers/firmware/efi/libstub/Makefile
> > > @@ -25,7 +25,7 @@ cflags-$(CONFIG_ARM)                := $(subst $(CC_FLAGS_FTRACE),,$(KBUILD_CFLAGS)) \
> > >                                  -fno-builtin -fpic \
> > >                                  $(call cc-option,-mno-single-pic-base)
> > >  cflags-$(CONFIG_RISCV)               := $(subst $(CC_FLAGS_FTRACE),,$(KBUILD_CFLAGS)) \
> > > -                                -fpic
> > > +                                -fpic $(DISABLE_STACKLEAK_PLUGIN)
> > >
> > >  cflags-$(CONFIG_EFI_GENERIC_STUB) += -I$(srctree)/scripts/dtc/libfdt
> > >
> > > --
> > > 2.36.1
> > >
>
>
>
> --
> Best Regards
>  Guo Ren



-- 
Best Regards
 Guo Ren

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