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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