Messages in this thread |  | | From | cp0613@linux ... | | Subject | Re: [PATCH] riscv: mm: Implement arch_within_stack_frames() for HARDENED_USERCOPY | | Date | Fri, 10 Apr 2026 20:26:07 +0800 |
| |
Hi Vivian,
Thank you very much for your review and suggestions.
On Fri, 10 Apr 2026 15:25:54 +0800, wangruikang@iscas.ac.cn wrote:
> On 4/10/26 09:50, cp0613@linux.alibaba.com wrote: > > From: Chen Pei <cp0613@linux.alibaba.com> > > > > Implement arch_within_stack_frames() to enable precise per-frame stack > > object validation for CONFIG_HARDENED_USERCOPY on RISC-V. > > > > == Background == > > > > [...] > > > > Signed-off-by: Chen Pei <cp0613@linux.alibaba.com> > > Patch message is probably too long. You can put additional information > like testing under a --- line to cut those out of the eventual actual > commit message. > > Make sure that Signed-off-by is above the cut if you do that.
Okay, that's really helpful advice, I've learned a lot.
> > --- > > arch/riscv/Kconfig | 1 + > > arch/riscv/include/asm/thread_info.h | 66 ++++++++++++++++++++++++++++ > > 2 files changed, 67 insertions(+) > > > > diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig > > index 6fe90591a274..4f765ff608d9 100644 > > --- a/arch/riscv/Kconfig > > +++ b/arch/riscv/Kconfig > > @@ -150,6 +150,7 @@ config RISCV > > select HAVE_ARCH_USERFAULTFD_MINOR if 64BIT && USERFAULTFD > > select HAVE_ARCH_USERFAULTFD_WP if 64BIT && MMU && USERFAULTFD && RISCV_ISA_SVRSW60T59B > > select HAVE_ARCH_VMAP_STACK if MMU && 64BIT > > + select HAVE_ARCH_WITHIN_STACK_FRAMES > > select HAVE_ASM_MODVERSIONS > > select HAVE_BUILDTIME_MCOUNT_SORT > > select HAVE_CONTEXT_TRACKING_USER > > diff --git a/arch/riscv/include/asm/thread_info.h b/arch/riscv/include/asm/thread_info.h > > index 36918c9200c9..616a41eb7416 100644 > > --- a/arch/riscv/include/asm/thread_info.h > > +++ b/arch/riscv/include/asm/thread_info.h > > @@ -101,6 +101,72 @@ struct thread_info { > > void arch_release_task_struct(struct task_struct *tsk); > > int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src); > > > > +#ifdef CONFIG_HAVE_ARCH_WITHIN_STACK_FRAMES > > Not needed since you've selected it above.
Okay, it seems that it's indeed not necessary.
> > +/* > > + * RISC-V stack frame layout (with frame pointer enabled): > > + * > > + * high addr > > + * +------------------+ <--- fp (s0) points here > > + * | saved ra | fp - 8 (return address) > > + * | saved fp | fp - 16 (previous frame pointer)
> fp - 2*sizeof(void*) probably, to account for RV32?
Yes, You are right. The implementation already uses 2 * sizeof(void *) to be RV32-compatible. However, the comments still hardcode. I'll update the comments to use fp - 2*sizeof(void*) to be architecture-neutral.
> > + * +------------------+ > > + * | local vars | > > + * | arguments | > > + * +------------------+ <--- sp > > + * low addr > > + * > > + * The struct stackframe { fp, ra } lives at (fp - sizeof(stackframe)), > > + * i.e. fp[-2]=saved_fp and fp[-1]=saved_ra. > > + * > > Maybe link to the authoritative source: > > https://github.com/riscv-non-isa/riscv-elf-psabi-doc/blob/master/riscv-cc.adoc#frame-pointer-convention
Okay, I will add this link.
> > + * For usercopy safety, we allow copies within [prev_fp, fp - 2*sizeof(void*)) > > + * for each frame in the chain, where prev_fp is the fp of the previous > > + * (lower) frame. This covers local variables and arguments but excludes > > + * the saved ra/fp slots at the top of the frame. > > + * > > + * We walk the frame chain starting from __builtin_frame_address(0) (the > > + * current frame), with prev_fp initialized to current_stack_pointer. > > + * Using current_stack_pointer -- rather than the 'stack' argument (which is > > + * the thread's entire stack base) -- ensures that objects in already-returned > > + * frames (address below current sp) are correctly detected as BAD_STACK, > > + * because no live frame in the chain will claim that region. > > + */ > > +__no_kmsan_checks > > +static inline int arch_within_stack_frames(const void * const stack, > > + const void * const stackend, > > + const void *obj, unsigned long len) > > +{ > > +#if defined(CONFIG_FRAME_POINTER) > > + const void *fp = (const void *)__builtin_frame_address(0); > > + const void *prev_fp = (const void *)current_stack_pointer; > > + > > + /* > > + * Walk the frame chain. Each iteration checks whether [obj, obj+len) > > + * falls within the local-variable area of the current frame: > > + * > > + * [prev_fp, fp - 2*sizeof(void*)) > > + * > > + * i.e. from the base of this frame (sp of this frame, which equals > > + * the fp of the frame below) up to (but not including) the saved > > + * fp/ra area at the top of this frame. > > + */ > > + while (stack <= fp && fp < stackend) { > > Since we access fp - 2 * sizeof(void *) below, this probably should be > something like this: > > while (stack + 2 * sizeof(void *) <= fp && fp < stackend) { > > (Possibly with some casts added.)
Thank you for pointing it out; I hadn't considered the potential for boundary violations here.
> > + const void *frame_vars_end = (const char *)fp - 2 * sizeof(void *); > > + > > + if (obj + len <= frame_vars_end) { > > + if (obj >= prev_fp) > > + return GOOD_FRAME; > > + return BAD_STACK; > > + } > > + prev_fp = fp; > > + fp = *(const void * const *)((const char *)fp - 2 * sizeof(void *)); > > Maybe: fp = *(const void * const *)frame_vars_end;
Yes, direct reuse.
> > + } > > + return BAD_STACK; > > +#else > > + return NOT_STACK; > > +#endif > > +} > > +#endif /* CONFIG_HAVE_ARCH_WITHIN_STACK_FRAMES */ > > + > > #endif /* !__ASSEMBLER__ */ > > > > /*
> Thanks, > Vivian "dramforever" Wang
Thanks, Pei
|  |