Messages in this thread | | | Subject | Re: [RFC PATCH v9 for 4.15 01/14] Restartable sequences system call | From | Florian Weimer <> | Date | Fri, 13 Oct 2017 15:56:15 +0200 |
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On 10/13/2017 03:40 PM, Mathieu Desnoyers wrote: > The proposed ABI does not require to store any function pointer. For a given > rseq_finish() critical section, pointers to specific instructions (within a > function) are emitted at link-time into a struct rseq_cs: > > struct rseq_cs { > RSEQ_FIELD_u32_u64(start_ip); > RSEQ_FIELD_u32_u64(post_commit_ip); > RSEQ_FIELD_u32_u64(abort_ip); > uint32_t flags; > } __attribute__((aligned(4 * sizeof(uint64_t)))); > > Then, at runtime, the fast-path stores the address of that struct rseq_cs > into the TLS struct rseq "rseq_cs" field. > > So all we store at runtime is a pointer to data, not a pointer to functions. > > But you seem to hint that having a pointer to data containing pointers to code > may still be making it easier for exploit writers. Can you elaborate on the > scenario ?
I'm concerned that the exploit writer writes a totally made up struct rseq_cs object into writable memory, along with function pointers, and puts the address of that in to the rseq_cs field.
This would be comparable to how C++ vtable pointers are targeted (including those in the glibc libio implementation of stdio streams).
Does this answer your questions?
Thanks, Florian
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