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xen/tools/misc/xen-detect.c
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Jan Beulich 6330e328ba tools/xen-detect: avoid possible pitfall with cpuid() 
The 64-bit form forces %ecx to 0 while the 32-bit one so far didn't - it
only ended up that way when "pv_context" is zero. While presently no
leaf queried by callers has separate subleaves, let's avoid chancing it.

While there
- replace references to operands by number,
- relax constraints where possible,
- limit PUSH/POP to just the registers not also used as input,
all where applicable also for the 64-bit variant.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Anthony PERARD <anthony.perard@citrix.com>
2022-01-06 16:12:15 +01:00

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8.2 KiB
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/******************************************************************************
* xen_detect.c
*
* Simple GNU C / POSIX application to detect execution on Xen VMM platform.
*
* Copyright (c) 2007, XenSource Inc.
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to
* deal in the Software without restriction, including without limitation the
* rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
* sell copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
* FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
* DEALINGS IN THE SOFTWARE.
*/
#define _GNU_SOURCE
#include <sys/types.h>
#include <sys/stat.h>
#include <limits.h>
#include <stdbool.h>
#include <stdint.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <setjmp.h>
#include <signal.h>
#include <unistd.h>
#include <getopt.h>
enum guest_type {
XEN_PV = 1,
XEN_HVM = 2,
XEN_NONE = 3
};
static const char *type;
static char *ver;
static void cpuid(uint32_t idx, uint32_t *regs, int pv_context)
{
#ifdef __i386__
/* Use the stack to avoid reg constraint failures with some gcc flags */
asm volatile (
"push %%ebx; push %%edx\n\t"
"test %[pv],%[pv] ; jz 1f ; ud2a ; .ascii \"xen\" ; 1: cpuid\n\t"
"mov %%eax,(%[regs]); mov %%ebx,4(%[regs])\n\t"
"mov %%ecx,8(%[regs]); mov %%edx,12(%[regs])\n\t"
"pop %%edx; pop %%ebx\n\t"
: "+a" (idx), "=c" (idx /* dummy */)
: "c" (0), [pv] "r" (pv_context), [regs] "SD" (regs)
: "memory" );
#else
asm volatile (
"test %[pv],%[pv] ; jz 1f ; ud2a ; .ascii \"xen\" ; 1: cpuid\n\t"
: "=a" (regs[0]), "=b" (regs[1]), "=c" (regs[2]), "=d" (regs[3])
: "0" (idx), "2" (0), [pv] "r" (pv_context) );
#endif
}
static int check_for_xen(int pv_context)
{
uint32_t regs[4];
char signature[13];
uint32_t base;
for ( base = 0x40000000; base < 0x40010000; base += 0x100 )
{
cpuid(base, regs, pv_context);
*(uint32_t *)(signature + 0) = regs[1];
*(uint32_t *)(signature + 4) = regs[2];
*(uint32_t *)(signature + 8) = regs[3];
signature[12] = '\0';
if ( !strcmp("XenVMMXenVMM", signature) && (regs[0] >= (base + 2)) )
goto found;
/* Higher base addresses are possible only with HVM. */
if ( pv_context )
break;
}
return 0;
found:
/*
* On CPUID faulting capable hardware even un-escaped CPUID will return
* the hypervisor leaves. Need to further distinguish modes.
*/
if ( !pv_context )
{
/*
* XEN_CPUID_FEAT1_MMU_PT_UPDATE_PRESERVE_AD is a PV-only feature
* pre-dating CPUID faulting support in Xen. Hence we can use it to
* tell whether we shouldn't report "success" to our caller here.
*/
cpuid(base + 2, regs, 0);
if ( regs[2] & (1u << 0) )
return 0;
}
cpuid(base + 1, regs, pv_context);
if ( regs[0] )
{
int r = asprintf(&ver, "V%u.%u", (uint16_t)(regs[0] >> 16),
(uint16_t)regs[0]);
if ( r < 0 )
{
perror("asprintf failed\n");
exit(EXIT_FAILURE);
}
}
return regs[0];
}
static jmp_buf sigill_jmp;
void sigill_handler(int sig)
{
longjmp(sigill_jmp, 1);
}
static void usage(void)
{
printf("Usage: xen_detect [options]\n");
printf("Options:\n");
printf(" -h, --help Display this information\n");
printf(" -q, --quiet Quiesce normal informational output\n");
printf(" -P, --pv Exit status 1 if not running as PV guest\n");
printf(" -H, --hvm Exit status 1 if not running as HVM or PVH guest.\n");
printf(" -N, --none Exit status 1 if running on Xen (PV or HVM)\n");
}
static bool check_dir(const char *filename)
{
FILE *f;
struct stat stab;
bool res;
f = fopen(filename, "r");
if ( !f )
return false;
res = !fstat(fileno(f), &stab) && S_ISDIR(stab.st_mode);
fclose(f);
return res;
}
static char *read_file_content(const char *filename)
{
FILE *f;
struct stat stab;
char *content = NULL;
int datalen;
f = fopen(filename, "r");
if ( !f )
return NULL;
if ( fstat(fileno(f), &stab) || !S_ISREG(stab.st_mode) ||
stab.st_size > INT_MAX || !stab.st_size )
goto out;
content = malloc(stab.st_size + 1);
if ( !content )
goto out;
/* For sysfs file, datalen is always PAGE_SIZE. 'read'
* will return the number of bytes of the actual content,
* rs <= datalen is expected.
*/
datalen = fread(content, 1, stab.st_size, f);
content[datalen] = 0;
if ( ferror(f) )
{
free(content);
content = NULL;
}
out:
fclose(f);
return content;
}
static enum guest_type check_sysfs(void)
{
char *str, *tmp;
enum guest_type res = XEN_NONE;
if ( !check_dir("/sys/hypervisor") )
return 0;
str = read_file_content("/sys/hypervisor/type");
if ( !str || strcmp(str, "xen\n") )
goto out;
free(str);
str = read_file_content("/sys/hypervisor/guest_type");
if ( !str )
return 0;
str[strlen(str) - 1] = 0;
type = str;
if ( !strcmp(type, "PV") )
res = XEN_PV;
else
res = XEN_HVM;
str = read_file_content("/sys/hypervisor/version/major");
if ( str )
str[strlen(str) - 1] = 0;
tmp = read_file_content("/sys/hypervisor/version/minor");
if ( tmp )
tmp[strlen(tmp) - 1] = 0;
if ( str && tmp )
{
int r = asprintf(&ver, "V%s.%s", str, tmp);
if ( r < 0 )
{
perror("asprintf failed\n");
exit(EXIT_FAILURE);
}
} else
ver = strdup("unknown version");
free(tmp);
out:
free(str);
return res;
}
int main(int argc, char **argv)
{
enum guest_type detected, expected = 0;
int ch, quiet = 0;
const static char sopts[] = "hqPHN";
const static struct option lopts[] = {
{ "help", 0, NULL, 'h' },
{ "quiet", 0, NULL, 'q' },
{ "pv", 0, NULL, 'P' },
{ "hvm", 0, NULL, 'H' },
{ "none", 0, NULL, 'N' },
{ 0, 0, 0, 0}
};
while ( (ch = getopt_long(argc, argv, sopts, lopts, NULL)) != -1 )
{
switch ( ch )
{
case 'q':
quiet = 1;
break;
case 'P':
expected = XEN_PV;
break;
case 'H':
expected = XEN_HVM;
break;
case 'N':
expected = XEN_NONE;
break;
default:
usage();
exit(1);
}
}
detected = check_sysfs();
if ( detected )
goto out;
/* Check for execution in HVM context. */
detected = XEN_HVM;
type = "HVM";
if ( check_for_xen(0) )
goto out;
/*
* Set up a signal handler to test the paravirtualised CPUID instruction.
* If executed outside Xen PV context, the extended opcode will fault, we
* will longjmp via the signal handler, and print "Not running on Xen".
*/
detected = XEN_PV;
type = "PV";
if ( !setjmp(sigill_jmp)
&& (signal(SIGILL, sigill_handler) != SIG_ERR)
&& check_for_xen(1) )
goto out;
detected = XEN_NONE;
out:
if ( quiet )
/* nothing */;
else if ( detected == XEN_NONE )
printf("Not running on Xen.\n");
else
printf("Running in %s context on Xen %s.\n", type, ver);
free(ver);
return expected && (expected != detected);
}
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