Re: [RFC PATCH for 4.18] rseq: use __u64 for rseq_cs fields, validate user inputs
flat view
From: Linus Torvalds <torvalds@linux-foundation.org>
Date: 2018-07-02 22:45:17
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On Mon, Jul 2, 2018 at 3:31 PM Mathieu Desnoyers [off-list ref] wrote:
Change the rseq ABI so rseq_cs start_ip, post_commit_offset and abort_ip fields are seen as 64-bit fields by both 32-bit and 64-bit kernels rather that ignoring the 32 upper bits on 32-bit kernels. This ensures we have a consistent behavior for a 32-bit binary executed on 32-bit kernels and in compat mode on 64-bit kernels.
Actually, now that I see this again, I react to:
quoted hunk ↗ jump to hunk
+static int check_rseq_cs_padding(struct task_struct *t) +{ + u32 pad; + int ret; + + ret = __get_user(pad, &t->rseq->rseq_cs_padding); + if (ret) + return ret; + if (pad) + return -EINVAL; + return 0; +}
This is all wrong.
Just make "rseq_cs" be an __u64" too. That will clean up everything,
and user space will have a much easier time filling it in too, since
it's just one field. Instead of having to remember about the "let's
fill in padding for 32-bit cases".
Then the rseq_get_rseq_cs() will be
__u64 rseq_cs;
ret = get_user(rseq_cs, &t->rseq->rseq_cs);
if (ret)
return ret;
ptr = (void *)rseq_cs;
if (rseq_cs != (unsigned long)ptr)
return -EINVAL;
and it's all good, no #ifdef's etc needed.
Hmm?
Sorry for the bike-shedding, but this is now the last remaining user
of that LINUX_FIELD_u32_u64, so let's just get rid of it entirely, ok?
Then we can also get rid of that silly uapi/linux/types_32_64.h header
file entirely.
That would be *lovely*. Simpler code, simpler and less error-prone
interfaces, and one less specialized header file.
Linus