On Tue, Jun 18, 2013 at 11:56:24PM +0800, 李春奇 <Arthur Chunqi Li> wrote:
> On Tue, Jun 18, 2013 at 11:47 PM, Gleb Natapov <gleb@xxxxxxxxxx> wrote:
> > On Tue, Jun 18, 2013 at 10:28:59PM +0800, Ê??Ê?•Â•? <Arthur Chunqi Li> wrote:
> >> On Tue, Jun 18, 2013 at 8:45 PM, Gleb Natapov <gleb@xxxxxxxxxx> wrote:
> >> > On Thu, Jun 13, 2013 at 05:30:03PM +0800, 李春奇 <Arthur Chunqi Li> wrote:
> >> >> Hi Gleb,
> >> >> I'm trying to solve these problems in the past days and meet many
> >> >> difficulties. You want to save all the general registers in calling
> >> >> insn_page, so registers should be saved to (save) in insn_page.
> >> >> Because all the instructions should be generated outside and copy to
> >> >> insn_page, and the instructions generated outside is RIP-relative, so
> >> >> inside insn_page (save) will be wrong pointed with RIP-relative code.
> >> >>
> >> > They do not have to be generated outside. You can write code into
> >> > insn_page directly. Something like this outside of any functions:
> >> >
> >> > asm(".align 4096\n\t"
> >> > ".global insn_page\n\t"
> >> > ".global insn_page_end\n\t"
> >> > ".global test_insn\n\t"
> >> > ".global test_insn_end\n\t"
> >> > "insn_page:"
> >> > "mov %%rax, outregs \n\t"
> >> > ...
> >> > "test_insn:\n\t"
> >> > "in (%ds), %al\n\t"
> >> > ". = . + 31\n\t"
> >> > "test_insn_end:\n\t"
> >> > "mov outregs, %%rax\n\t"
> >> > ...
> >> > "ret\n\t"
> >> > ".align 4096\n\t"
> >> > "insn_page_end:\n\t");
> >> >
> >> > Now you copy that into alt_insn_page, put instruction you want to test
> >> > into test_insn offset and remap alt_insn_page into "insn_page" virtual address.
> >> I used such codes:
> >>
> >> invlpg((void *)virt_to_phys(insn_page));
> > virt_to_phys?
> This is a mistake, I changed it to "invlpg(insn_page)" but the result
> is the same.
> >
> >> asm volatile("call *%0" : : "r"(insn_page));
> >> install_page(cr3, virt_to_phys(alt_insn_page), insn_page);
> >> asm volatile("call *%0": : "r"(insn_page+1));
> > +1?
> Here I put "ret" on the first byte of insn_page, so the first call of
> "insn_page" can just return, and the second call of "insn_page+1“ will
> directly call the second byte, which is the real content of insn_page.
Send the code.
--
Gleb.
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