Add a tboot command line option that falls back to booting the kernel
directly instead of performing a measured launch, if the previous measured
launch failed.
This acts as a failsafe and prevents the system from going into an endless
reboot loop.
Testing:
Disable Vt-d on system. Boot without ignore_prev_err, and with
ignore_prev_err=true. Verify system keeps trying to boot and resets on SENTER.
Set ignore_prev_err=false. Verify tboot skips measured launch and transfers
control directly to the kernel. Soft reset system and verify error is not
cleared.
Power-cycle system and verify TXT error is cleared.
Signed-off-by: Sahil Rihan <sri...@fb.com>
diff --git a/README b/README
--- a/README
+++ b/README
@@ -272,6 +272,25 @@
It means tboot will use this algorithm to compute hash and use
TPM2_PCR_Extend
to extend it into PCRs.
+o Recovering from measured launch failures.
+ When there's an error during SENTER, the system usually reboots. Since the
underlying
+ cause is some sort of configuration error, the system can end up in a loop
+ rebooting endlessly after each attempted measured launch. In some
environments it
+ make more sense to fall back to booting the kernel directly so that the
system comes
+ up and is remotely accessible. After that the issue can be diagnosed and
the system
+ power-cycled to clear the error. To enable this behavior a command line
option can
+ be used:
+ ignore_prev_err=false|true // defaults to true
+
+ The option defaults to true, which preserves the original behavior i.e. try
a measured
+ launch even if the previous measured launch had errors.
+
+ Setting the value to false will check if the previous measured launch was
successful
+ by inspecting the TXT.ERRORCODE value. If measured launch failed, tboot
will launch
+ the kernel directly without trying to perform a measured launch.
+
+ Note: TXT.ERRORCODE is only cleared if the system is power cycled. A reboot
is not
+ sufficient to clear the error code.
PCR Usage:
---------
diff --git a/include/tb_error.h b/include/tb_error.h
--- a/include/tb_error.h
+++ b/include/tb_error.h
@@ -66,6 +66,7 @@
TB_ERR_FATAL, /* generic fatal error */
TB_ERR_NV_VERIFICATION_FAILED, /* NV failed to verify against
policy */
+ TB_ERR_PREV_TXT_ERROR, /* previous measured launch failed
*/
TB_ERR_MAX
} tb_error_t;
diff --git a/tboot/common/cmdline.c b/tboot/common/cmdline.c
--- a/tboot/common/cmdline.c
+++ b/tboot/common/cmdline.c
@@ -83,7 +83,8 @@
{ "min_ram", "0" }, /* size in bytes | 0 for no min */
{ "call_racm", "false" }, /* true|false|check */
{ "measure_nv", "false" }, /* true|false */
- { "extpol", "sha1" }, /* agile|embedded|sha1|sha256|sm3|... */
+ { "extpol", "sha1" }, /* agile|embedded|sha1|sha256|sm3|... */
+ { "ignore_prev_err", "true"}, /* true|false */
{ NULL, NULL }
};
static char
g_tboot_param_values[ARRAY_SIZE(g_tboot_cmdline_options)][MAX_VALUE_LEN];
@@ -528,6 +529,15 @@
}
}
+bool get_tboot_ignore_prev_err(void)
+{
+ const char *ignore_prev_err = get_option_val(g_tboot_cmdline_options,
+ g_tboot_param_values,
"ignore_prev_err");
+ if ( ignore_prev_err == NULL || strcmp(ignore_prev_err, "true") == 0 )
+ return true;
+ return false;
+}
+
/*
* linux kernel command line parsing
*/
diff --git a/tboot/common/policy.c b/tboot/common/policy.c
--- a/tboot/common/policy.c
+++ b/tboot/common/policy.c
@@ -97,6 +97,7 @@
{ TB_POLTYPE_CONT_NON_FATAL, TB_POLACT_CONTINUE,
{
{TB_ERR_FATAL, TB_POLACT_HALT},
+ {TB_ERR_PREV_TXT_ERROR, TB_POLACT_UNMEASURED_LAUNCH},
{TB_ERR_TPM_NOT_READY, TB_POLACT_UNMEASURED_LAUNCH},
{TB_ERR_SMX_NOT_SUPPORTED, TB_POLACT_UNMEASURED_LAUNCH},
{TB_ERR_VMX_NOT_SUPPORTED, TB_POLACT_UNMEASURED_LAUNCH},
diff --git a/tboot/common/tb_error.c b/tboot/common/tb_error.c
--- a/tboot/common/tb_error.c
+++ b/tboot/common/tb_error.c
@@ -114,6 +114,9 @@
case TB_ERR_NV_VERIFICATION_FAILED:
printk(TBOOT_ERR"verifying nv against policy failed.\n");
break;
+ case TB_ERR_PREV_TXT_ERROR:
+ printk(TBOOT_ERR"previous measured launch had errors, skipping
measured launch...\n");
+ break;
default:
printk(TBOOT_ERR"unknown error (%d).\n", error);
break;
diff --git a/tboot/common/tboot.c b/tboot/common/tboot.c
--- a/tboot/common/tboot.c
+++ b/tboot/common/tboot.c
@@ -414,7 +414,10 @@
apply_policy(err);
/* print any errors on last boot, which must be from TXT launch */
- txt_get_error();
+ txt_display_errors();
+ if (txt_has_error() && get_tboot_ignore_prev_err() == false) {
+ apply_policy(TB_ERR_PREV_TXT_ERROR);
+ }
/* need to verify that platform can perform measured launch */
err = verify_platform();
diff --git a/tboot/include/cmdline.h b/tboot/include/cmdline.h
--- a/tboot/include/cmdline.h
+++ b/tboot/include/cmdline.h
@@ -54,6 +54,7 @@
extern bool get_tboot_call_racm_check(void);
extern bool get_tboot_measure_nv(void);
extern void get_tboot_extpol(void);
+extern bool get_tboot_ignore_prev_err(void);
/* for parse cmdline of linux kernel, say vga and mem */
extern void linux_parse_cmdline(const char *cmdline);
diff --git a/tboot/include/txt/txt.h b/tboot/include/txt/txt.h
--- a/tboot/include/txt/txt.h
+++ b/tboot/include/txt/txt.h
@@ -39,7 +39,8 @@
// #include <multiboot.h>
extern bool txt_is_launched(void);
-extern bool txt_get_error(void);
+extern void txt_display_errors(void);
+extern bool txt_has_error(void);
extern void txt_get_racm_error(void);
extern tb_error_t supports_txt(void);
extern tb_error_t txt_verify_platform(void);
diff --git a/tboot/txt/errors.c b/tboot/txt/errors.c
--- a/tboot/txt/errors.c
+++ b/tboot/txt/errors.c
@@ -46,7 +46,7 @@
#include <txt/errorcode.h>
-static void display_errors(void)
+void txt_display_errors(void)
{
txt_errorcode_t err;
txt_ests_t ests;
@@ -58,7 +58,7 @@
* display TXT.ERRORODE error
*/
err = (txt_errorcode_t)read_pub_config_reg(TXTCR_ERRORCODE);
- if (err._raw == 0 || err._raw == 0xc0000001 || err._raw == 0xc0000009)
+ if (txt_has_error() == false)
printk(TBOOT_INFO"TXT.ERRORCODE: 0x%Lx\n", err._raw);
else
printk(TBOOT_ERR"TXT.ERRORCODE: 0x%Lx\n", err._raw);
@@ -112,17 +112,16 @@
printk(TBOOT_ERR"TXT.E2STS: 0x%Lx\n", e2sts._raw);
}
-bool txt_get_error(void)
+bool txt_has_error(void)
{
txt_errorcode_t err;
- display_errors();
-
err = (txt_errorcode_t)read_pub_config_reg(TXTCR_ERRORCODE);
- if ( err.valid )
+ if (err._raw == 0 || err._raw == 0xc0000001 || err._raw == 0xc0000009) {
return false;
- else
+ } else {
return true;
+ }
}
#define CLASS_ACM_ENTRY 0x1
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