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Improvements for running biosdevname in virtual machines #12

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2f51429
Add an option to allow running in virtual machines
dmbaturin Sep 21, 2023
2246948
Limit the cpuid hypervisor bit check to x86 machines
dmbaturin Sep 21, 2023
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49 changes: 31 additions & 18 deletions src/bios_dev_name.c
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Original file line number Diff line number Diff line change
Expand Up @@ -15,6 +15,7 @@

static struct bios_dev_name_opts opts;
int nopirq;
int allow_vm;
int smver_mjr;
int smver_mnr;
int is_valid_smbios = 0;
Expand All @@ -29,6 +30,7 @@ static void usage(void)
fprintf(stderr, " -P or --prefix [string] string use for embedded NICs (default='em')\n");
fprintf(stderr, " -s or --smbios [x.y] Require SMBIOS x.y or greater\n");
fprintf(stderr, " -x or --nopirq Don't use $PIR table for slot numbers\n");
fprintf(stderr, " -V or --allow-vm Allow running in virtual machines\n");
fprintf(stderr, " -v or --version Show biosdevname version\n");
fprintf(stderr, " Example: biosdevname -i eth0\n");
fprintf(stderr, " returns: em1\n");
Expand Down Expand Up @@ -64,11 +66,12 @@ parse_opts(int argc, char **argv)
{"prefix", required_argument, 0, 'P'},
{"nopirq", no_argument, 0, 'x'},
{"smbios", required_argument, 0, 's'},
{"allow-vm", no_argument, 0, 'V'},
{"version", no_argument, 0, 'v'},
{0, 0, 0, 0}
};
c = getopt_long(argc, argv,
"dip:P:xs:v",
"dip:P:xs:Vv",
long_options, &option_index);
if (c == -1)
break;
Expand All @@ -91,6 +94,9 @@ parse_opts(int argc, char **argv)
case 'x':
nopirq = 1;
break;
case 'V':
allow_vm = 1;
break;
case 'v':
fprintf(stderr, "biosdevname version %s\n", BIOSDEVNAME_VERSION);
exit(0);
Expand All @@ -113,28 +119,33 @@ parse_opts(int argc, char **argv)
static u_int32_t
cpuid (u_int32_t eax, u_int32_t ecx)
{
asm volatile (
"xor %%ebx, %%ebx; cpuid"
: "=a" (eax), "=c" (ecx)
: "a" (eax)
: "%ebx", "%edx");
return ecx;
#if defined(__x86_64__) || defined(__i386__)
asm volatile (
"xor %%ebx, %%ebx; cpuid"
: "=a" (eax), "=c" (ecx)
: "a" (eax)
: "%ebx", "%edx");
return ecx;
#else
return 0;
#endif
}

/*
Algorithm suggested by:
http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=1009458
*/

static int
running_in_virtual_machine (void)
{
u_int32_t eax=1U, ecx=0U;

ecx = cpuid (eax, ecx);
if (ecx & 0x80000000U)
return 1;
#if defined(__x86_64__) || defined(__i386__)
/* Algorithm suggested by https://kb.vmware.com/s/article/1009458 */
u_int32_t eax=1U, ecx=0U;

ecx = cpuid (eax, ecx);
if (ecx & 0x80000000U)
return 1;
else
return 0;
#else
return 0;
#endif
}

static int
Expand All @@ -158,8 +169,10 @@ int main(int argc, char *argv[])

if (!running_as_root())
exit(3);
if (running_in_virtual_machine())
if (!allow_vm && running_in_virtual_machine()) {
fprintf(stderr, "Refusing to run in a virtual machine without --allow-vm option\n");
exit(4);
}
cookie = setup_bios_devices(opts.namingpolicy, opts.prefix);
if (!cookie) {
rc = 1;
Expand Down