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    SubjectRe: [RFC PATCH v9 for 4.15 01/14] Restartable sequences system call
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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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