Re: Trusted Boot with OpenBSD
Patching the assembly code is the work of Julius Zint -
not my work. I have only patched the patch files because
some of the old one doesn't work anymore. This is because
of some changes of OpenBSDs source code which are preventing
the patch util to find the lines to change.
‐‐‐ Original Message ‐‐‐
Am Mittwoch, 21. April 2021 21:17 schrieb :
> That's very interesting, and good work patching the assembly code.
>
> On Wed, Apr 21, 2021 at 08:26:18AM +, podolica wrote:
>
> > Hi all,
> > I have tested if the trusted boot implementation
> > of Julius Zint for OpenBSD 6.5
> > (https://marc.info/?l=openbsd-misc=158255450604977=2)
> > is still working in OpenBSD 6.8.
> > Despite of some patch files that had to be updated,
> > all changes needed to be applied can be applied and
> > Trusted Boot can be used.
> > (Tested with an external hard drive and an amd64
> > ThinkPad with TPM module version 1.2)
> > Here are the new patch files. I did not provide them as
> > attachments because the netiquette says only the bugs,
> > ports and the tech mailing list are supporting
> > attachments although it was allowed when Julius Zint
> > made it's initial post. The files are beginning after
> > the `and are ending before the next` just like
> > in Markdown.
> >
> > gidt.S.patch
> >
> > =
> >
> > --- gidt.S.orig Mon Apr 19 13:22:32 2021
> > +++ gidt.S Mon Apr 19 13:22:32 2021
> > @@ -432,11 +432,13 @@
> > movl%edi, _C_LABEL(BIOS_regs)+BIOSR_DI
> >
> > /* clear NT flag in eflags */
> > - pushf
> > + push%eax
> > + pushf
> > pop %eax
> > and $0xbfff, %eax
> > push%eax
> > popf
> > + pop %eax
> >
> > pop %gs
> > pop %fs
> >
> >
> >
> > cmd_i386.c.patch
> >
> > =
> >
> > --- cmd_i386.c.orig Mon Apr 19 13:23:44 2021
> > +++ cmd_i386.c Mon Apr 19 13:23:44 2021
> > @@ -36,6 +36,7 @@
> > #include "biosdev.h"
> > #include "libsa.h"
> > #include
> > +#include
> >
> > extern const char version[];
> >
> > @@ -44,6 +45,7 @@
> > int Xdiskinfo(void);
> > int Xmemory(void);
> > int Xregs(void);
> > +int Xtpm(void);
> >
> > /* From gidt.S */
> > int bootbuf(void *, int);
> > @@ -53,11 +55,155 @@
> > { "comaddr",CMDT_CMD, Xcomaddr },
> > { "diskinfo", CMDT_CMD, Xdiskinfo },
> > { "memory", CMDT_CMD, Xmemory },
> > +{ "tpm",CMDT_CMD, Xtpm },
> > #ifdef DEBUG
> > { "regs", CMDT_CMD, Xregs },
> > #endif
> > { NULL, 0 }
> > };
> > +
> > +/**
> > + * print_memory - debugging functionality to dump memory region to
> > screen
> > + * @buf:memory location to begin dump
> > + * @rows: rows to print
> > + * @columns:columns to print
> > + *
> > + * Remarks: total bytes dumped = rows * columns
> > + */
> > +void
> > +print_memory(void* buf, uint32_t rows, uint32_t columns)
> > +{
> > +uint8_t* iter = buf;
> > +for(int i = 0; i < rows; i++) {
> > +printf("%03x:", i * columns);
> > +for(int k = 0; k < columns; k++) {
> > +printf(" %02x", *iter);
> > +iter++;
> > +}
> > +printf("\\n");
> > +}
> > +}
> > +
> > +#define SECRET_BLK_OFF 1
> > +
> > +int
> > +Xtpm(void)
> > +{
> > +int rc;
> > +uint8_t major = 0;
> > +uint8_t minor = 0;
> > +rc = tpm_statuscheck(, );
> > + if(rc != 0) {
> > +printf("No TCG compliant BIOS available.\\n");
> > + }
> > + else if(major != 1 && minor != 2) {
> > +printf("Incompatible TCG BIOS version: %u.%u\\n",
> > major, minor);
> > + }
> > + if (cmd.argc < 2) {
> > +printf("machine tpm r[andom]|p[cr]|u[nseal]
> > [DiskNumber]|s[eal] secret [DiskNumber]\\n");
> > +printf("strlen(secret) <= 100\\n");
> > +return 0;
> > +}
> > +switch(cmd.argv[1][0]) {
> > +case 'r': {
> > +char random_buf[20];
> > +tpm_random(random_buf, 20);
> > +print_memory(random_buf, 2, 10);
> > +} break;
> > +case 'p': {
> > +tpm_printpcr(0, 15);
> > +} break;
> > +case 'u': {
> > +// load secret disk block
> > +int disk_number = 0x80;
> > +if(cmd.argc == 3) {
> > +disk_number = (int)strtol(cmd.argv[2], NULL, 0);
> > +
Re: Trusted Boot with OpenBSD
That's very interesting, and good work patching the assembly code.
On Wed, Apr 21, 2021 at 08:26:18AM +, podolica wrote:
Hi all,
I have tested if the trusted boot implementation
of Julius Zint for OpenBSD 6.5
(https://marc.info/?l=openbsd-misc=158255450604977=2)
is still working in OpenBSD 6.8.
Despite of some patch files that had to be updated,
all changes needed to be applied can be applied and
Trusted Boot can be used.
(Tested with an external hard drive and an amd64
ThinkPad with TPM module version 1.2)
Here are the new patch files. I did not provide them as
attachments because the netiquette says only the bugs,
ports and the tech mailing list are supporting
attachments although it was allowed when Julius Zint
made it's initial post. The files are beginning after
the ``` and are ending before the next ``` just like
in Markdown.
# gidt.S.patch
```
--- gidt.S.orig Mon Apr 19 13:22:32 2021
+++ gidt.S Mon Apr 19 13:22:32 2021
@@ -432,11 +432,13 @@
movl%edi, _C_LABEL(BIOS_regs)+BIOSR_DI
/* clear NT flag in eflags */
- pushf
+ push%eax
+ pushf
pop %eax
and $0xbfff, %eax
push%eax
popf
+ pop %eax
pop %gs
pop %fs
```
# cmd_i386.c.patch
```
--- cmd_i386.c.orig Mon Apr 19 13:23:44 2021
+++ cmd_i386.c Mon Apr 19 13:23:44 2021
@@ -36,6 +36,7 @@
#include "biosdev.h"
#include "libsa.h"
#include
+#include
extern const char version[];
@@ -44,6 +45,7 @@
int Xdiskinfo(void);
int Xmemory(void);
int Xregs(void);
+int Xtpm(void);
/* From gidt.S */
int bootbuf(void *, int);
@@ -53,11 +55,155 @@
{ "comaddr", CMDT_CMD, Xcomaddr },
{ "diskinfo", CMDT_CMD, Xdiskinfo },
{ "memory", CMDT_CMD, Xmemory },
+{ "tpm",CMDT_CMD, Xtpm },
#ifdef DEBUG
{ "regs", CMDT_CMD, Xregs },
#endif
{ NULL, 0 }
};
+
+/**
+ * print_memory - debugging functionality to dump memory region to screen
+ * @buf:memory location to begin dump
+ * @rows: rows to print
+ * @columns:columns to print
+ *
+ * Remarks: total bytes dumped = rows * columns
+ */
+void
+print_memory(void* buf, uint32_t rows, uint32_t columns)
+{
+uint8_t* iter = buf;
+for(int i = 0; i < rows; i++) {
+printf("%03x:", i * columns);
+for(int k = 0; k < columns; k++) {
+printf(" %02x", *iter);
+iter++;
+}
+printf("\n");
+}
+}
+
+#define SECRET_BLK_OFF 1
+
+int
+Xtpm(void)
+{
+int rc;
+uint8_t major = 0;
+uint8_t minor = 0;
+rc = tpm_statuscheck(, );
+ if(rc != 0) {
+printf("No TCG compliant BIOS available.\n");
+ }
+ else if(major != 1 && minor != 2) {
+printf("Incompatible TCG BIOS version: %u.%u\n", major, minor);
+ }
+ if (cmd.argc < 2) {
+printf("machine tpm r[andom]|p[cr]|u[nseal] [DiskNumber]|s[eal]
secret [DiskNumber]\n");
+printf("strlen(secret) <= 100\n");
+return 0;
+}
+switch(cmd.argv[1][0]) {
+case 'r': {
+char random_buf[20];
+tpm_random(random_buf, 20);
+print_memory(random_buf, 2, 10);
+} break;
+case 'p': {
+tpm_printpcr(0, 15);
+} break;
+case 'u': {
+// load secret disk block
+int disk_number = 0x80;
+if(cmd.argc == 3) {
+disk_number = (int)strtol(cmd.argv[2], NULL, 0);
+}
+unsigned char* secret_disk_block = alloc(512);
+memset(secret_disk_block, 0x00, 512);
+struct diskinfo * disk_info = dklookup(disk_number);
+if(disk_info == NULL) {
+printf("IO Error - Disk %x not found\n", disk_number);
+goto unseal_end;
+}
+rc = biosd_diskio(F_READ, disk_info, SECRET_BLK_OFF, 1,
secret_disk_block);
+if(rc != 0) {
+printf("IO Error \n");
+goto unseal_end;
+}
+if (secret_disk_block[0] != 'A' ||
+secret_disk_block[1] != 'E' ||
+secret_disk_block[2] != 'M' ||
+secret_disk_block[3] != 'S')
+{
+printf("No sealed secret found on disk");
+goto unseal_end;
+}
+uint32_t sealed_size = *((uint32_t*)(secret_disk_block + 4));
+unsigned char* sealed_data = secret_disk_block + 8;
+if(sealed_size > 512) {
+printf("Invalid size for sealed data\n");
+goto unseal_end;
+}
+
+//
Re: Trusted Boot with OpenBSD
>> I can't tell from the instructions how the FDE encryption key is stored -- >> do we manually seal it to the TPM and then manually unseal and copy/paste it >> every time we boot? Or is it assumed the user will write a script to handle >> this -- a script which itself will have to be measured by the TPM? > > This is not possible with the current version. The Masterthesis was > about answering this Question: Did unencrypted software change since > the last time the user operated this system. > > What exactly is your use case? Do you want a system with FDE that does > not prompt you for the encryption key or do you want to improve the > security by storing a part of the key material inside the TPM while the > other half is provided by a user password? > > There are a lot of possibilities with a available TPM on boot, so if > you have a specific use case we can tailor that right in. > > Before we do that i think it is important to make this feature a lot > easier to install. Following this manual, patching and compiling source > code and updating the MBR and biosboot is not something the user should > have to worry about. > > The problem is, in order to make space for this feature in the MBR as > well as in biosboot i had to remove the code responsible for loading a > block from disk via CHS. This is obviously not acceptable if this should > be integrated back into OpenBSD. > > One possible solution would be to let the MBR and biosboot grow bigger > than 512 byte and let installboot(8) figure out what the user needs and > remove code paths that are not used to get the binary back to 512 byte. > > Everything else i thought of involves recompiling.
Re: Trusted Boot with OpenBSD
On Mon, Feb 24, 2020 at 03:22:28PM +0100, Julius Zint wrote: boot(8) supports the machine specific command "tpm". This allows a user to: 1: read the current contents of the Platform Control Registers (PCR) with the "pcr" parameter machine tpm p[cr] 2: seal a user supplied secret to the current PCR values and store it in the second block on a disk, that can be altered via a parameter. WARNING: If there is any other data in this block, it will be overwritten without asking again. machine tpm s[eal] secret [DiskNumber] 3: unseal a previously sealed secrent and display it to the user. This command just reads the second block of the disk that can be specified by the user and unseals it via the TPM machine tpm u[nseal] [DiskNumber] I hope you are enjoying your (well-earned) vacation. I can't tell from the instructions how the FDE encryption key is stored -- do we manually seal it to the TPM and then manually unseal and copy/paste it every time we boot? Or is it assumed the user will write a script to handle this -- a script which itself will have to be measured by the TPM?
