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add C program to get hardware capabilities from CPUID

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Implement a C program that extracts AMD SEV hardware information such
as reduced-phys-bios and cbitpos from CPUID, looks if SEV, SEV-ES &
SEV-SNP are enabled, and outputs these details as JSON to
/run/qemu-server/host-hw-capabilities.json

This program can also be used to read and save other hardware
information.

Signed-off-by: Markus Frank <m.frank@proxmox.com>
Co-authored-by: Thomas Lamprecht <t.lamprecht@proxmox.com>
Reviewed-by: Fiona Ebner <f.ebner@proxmox.com>
This commit is contained in:
Markus Frank 2024-11-11 14:57:09 +01:00 committed by Thomas Lamprecht
parent 1ceb26e71e
commit c9eee44b47
3 changed files with 98 additions and 0 deletions
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1
Makefile
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@ -65,6 +65,7 @@ install: $(PKGSOURCES)
install -m 0644 -D bootsplash.jpg $(DESTDIR)/usr/share/$(PACKAGE)
$(MAKE) -C PVE install
$(MAKE) -C qmeventd install
$(MAKE) -C query-machine-capabilities install
$(MAKE) -C qemu-configs install
$(MAKE) -C vm-network-scripts install
install -m 0755 qm $(DESTDIR)$(SBINDIR)

18
query-machine-capabilities/Makefile Normal file
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@ -0,0 +1,18 @@
DESTDIR=
PREFIX=/usr
BINDIR=${PREFIX}/libexec/qemu-server
CC ?= gcc
CFLAGS += -O2 -fanalyzer -Werror -Wall -Wextra -Wpedantic -Wtype-limits -Wl,-z,relro -std=gnu11
query-machine-capabilities: query-machine-capabilities.c
$(CC) $(CFLAGS) -o $@ $< $(LDFLAGS)
.PHONY: install
install: query-machine-capabilities
install -d ${DESTDIR}/${BINDIR}
install -m 0755 query-machine-capabilities ${DESTDIR}${BINDIR}
.PHONY: clean
clean:
rm -f query-machine-capabilities

79
query-machine-capabilities/query-machine-capabilities.c Normal file
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@ -0,0 +1,79 @@
#include <stdio.h>
#include <stdint.h>
#include <stdbool.h>
#include <sys/stat.h>
#include <errno.h>
#include <string.h>
int main() {
uint32_t eax, ebx, ecx, edx;
// query Encrypted Memory Capabilities, see:
// https://en.wikipedia.org/wiki/CPUID#EAX=8000001Fh:_Encrypted_Memory_Capabilities
uint32_t query_function = 0x8000001F;
asm volatile("cpuid"
: "=a"(eax), "=b"(ebx), "=c"(ecx), "=d"(edx)
: "0"(query_function)
);
bool sev_support = (eax & (1<<1)) != 0;
bool sev_es_support = (eax & (1<<3)) != 0;
bool sev_snp_support = (eax & (1<<4)) != 0;
uint8_t cbitpos = ebx & 0x3f;
uint8_t reduced_phys_bits = (ebx >> 6) & 0x3f;
const char *path = "/run/qemu-server/";
// Check that the directory exists and create it if it does not.
struct stat statbuf;
int ret = stat(path, &statbuf);
if (ret == 0) {
if (!S_ISDIR(statbuf.st_mode)) {
printf("Path %s is not a directory.\n", path);
return 1;
}
} else if (errno == ENOENT) {
if (mkdir(path, 0755) != 0) {
printf("Error creating directory %s: %s\n", path, strerror(errno));
return 1;
}
} else {
printf("Error checking path %s: %s\n", path, strerror(errno));
return 1;
}
FILE *file;
const char *filename = "/run/qemu-server/host-hw-capabilities.json";
file = fopen(filename, "w");
if (file == NULL) {
perror("Error opening file");
return 1;
}
ret = fprintf(file,
"{"
" \"amd-sev\": {"
" \"cbitpos\": %u,"
" \"reduced-phys-bits\": %u,"
" \"sev-support\": %s,"
" \"sev-support-es\": %s,"
" \"sev-support-snp\": %s"
" }"
" }\n",
cbitpos,
reduced_phys_bits,
sev_support ? "true" : "false",
sev_es_support ? "true" : "false",
sev_snp_support ? "true" : "false"
);
if (ret < 0) {
printf("Error writing to file %s: %s\n", path, strerror(errno));
}
ret = fclose(file);
if (ret != 0) {
printf("Error closing file %s: %s\n", path, strerror(errno));
}
return 0;
}