After step by step monitoring, I get the following statistics about hypercall
entries:
numbers | hypercalls | executed bytes (offset to hypercall entry) 7755 24: 0
1 3 8 a c d 6374 23: 0 1 3 4 9 3281 25: 0 1 3 8 a c d 2979 13: 0 1 3 8 a
c d 2475 17: 0 1 3 8 2253 17: a c d 749 3: 0 1 3 8 a c d 655 23: 0 1
3 4 9 0 1 3 4 9 640 29: 0 1 3 8 636 29: a c d 445 23: 0 1 3 4 9 0 1 3
4 9 0 1 3 4 9 433 23: 0 1 3 4 9 0 1 3 4 9 0 1 3 4 9 0 1 3 4 9 414 24: 0 1
3 8 a c d 0 1 3 8 a c d 274 13: 0 1 3 8 8 a c d 129 17: d 125 17: a c
112 29: a c d 0 1 3 8 112 17: c d 105 17: a 73 24: 0 1 3 8 a c d 0
1 3 8 a c d 0 1 3 8 a c d 67 17: 0 59 17: 8 a c d 54 17: 0 1 3
53 17: 0 1 50 17: 1 3 8 a c d 46 17: 3 8 a c d 21 3: 0 1 3 8 a c d
0 1 3 8 a c d 8 33: 0 1 3 8 a c d 7 17: 1 3 6 13: 0 1 3 8 8 8 a
c d 5 29: d 5 23: 0 1 3 4 9 0 1 3 4 9 0 1 3 4 9 0 1 3 4 9 0 1 3 4 9
4 29: a c 4 17: 3 3 17: 8 a 3 17: 8 3 17: 3 8 3 17:
1 3 8 a c 3 17: 1 2 29: 0 1 3 8 a c d 2 17: 3 8 a 2 17: 1 3
8 a 2 17: 1 3 8 1 29: c 1 29: a 1 29: 3 8 a c d 1 29:
1 3 8 a c d 1 29: 0 1 1 29: 0 1 17: 3 8 a c
From the above we can see that hypercall #17 and #29 are very irregular, with
various combination occurs. Other hypercalls basically obey to the sequence of
"0 1 3 8 a c d" which conforms to the content in hypercall_page_initialise
function. HYPERCALL_iret is a special one as explained in the function, but it
also conforms to its sequence of "0 1 3 4 9". So why would #17(do_xen_version)
and #29(do_sched_op) performs irregular? They seem to be easily interrupted at
any place of the hypercall entry. Besides, there is also some abnormals for
#13(do_multicall) shown in bold.
From: quizy_jo...@outlook.com
To: xen-de...@lists.xenproject.org
Date: Wed, 2 Mar 2016 12:44:16 +0000
Subject: Re: [Xen-devel] what's inside hypercall page?
For following hypercall page initialise code, where would the execution jumps
at syscall? How can I predict what is the execution order of "pop %r11"? Is it
the fifth instruction/step? I need the order to precisely set up hooks to
monitor hypercalls.
static void hypercall_page_initialise_ring3_kernel(void *hypercall_page){
char *p; int i;
/* Fill in all the transfer points with template machine code. */ for (
i = 0; i < (PAGE_SIZE / 32); i++ ) { if ( i == __HYPERVISOR_iret )
continue;
p = (char *)(hypercall_page + (i * 32)); *(u8 *)(p+ 0) = 0x51;
/* push %rcx */ *(u16 *)(p+ 1) = 0x5341; /* push %r11 */ *(u8
*)(p+ 3) = 0xb8; /* mov $<i>,%eax */ *(u32 *)(p+ 4) = i;
*(u16 *)(p+ 8) = 0x050f; /* syscall */ *(u16 *)(p+10) = 0x5b41; /* pop
%r11 */ *(u8 *)(p+12) = 0x59; /* pop %rcx */ *(u8 *)(p+13)
= 0xc3; /* ret */ }
/* * HYPERVISOR_iret is special because it doesn't return and expects a
* special stack frame. Guests jump at this transfer point instead of *
calling it. */ p = (char *)(hypercall_page + (__HYPERVISOR_iret * 32));
*(u8 *)(p+ 0) = 0x51; /* push %rcx */ *(u16 *)(p+ 1) = 0x5341; /*
push %r11 */ *(u8 *)(p+ 3) = 0x50; /* push %rax */ *(u8 *)(p+ 4) =
0xb8; /* mov $__HYPERVISOR_iret,%eax */ *(u32 *)(p+ 5) =
__HYPERVISOR_iret; *(u16 *)(p+ 9) = 0x050f; /* syscall */
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