feat(drtm): prepare EL state during dynamic launch
Prepared EL state before dynamic launch
Change-Id: I3940cd7fc74da1a1addbeb08ae34f16771395e61
Signed-off-by: Manish Pandey <manish.pandey2@arm.com>
Signed-off-by: Lucian Paul-Trifu <lucian.paultrifu@gmail.com>
diff --git a/services/std_svc/drtm/drtm_main.c b/services/std_svc/drtm/drtm_main.c
index ad2b774..9237d82 100644
--- a/services/std_svc/drtm/drtm_main.c
+++ b/services/std_svc/drtm/drtm_main.c
@@ -21,6 +21,7 @@
#include "drtm_main.h"
#include "drtm_measurements.h"
#include "drtm_remediation.h"
+#include <lib/el3_runtime/context_mgmt.h>
#include <lib/psci/psci_lib.h>
#include <lib/xlat_tables/xlat_tables_v2.h>
#include <plat/common/platform.h>
@@ -446,11 +447,107 @@
return SUCCESS;
}
+static void drtm_dl_reset_dlme_el_state(enum drtm_dlme_el dlme_el)
+{
+ uint64_t sctlr;
+
+ /*
+ * TODO: Set PE state according to the PSCI's specification of the initial
+ * state after CPU_ON, or to reset values if unspecified, where they exist,
+ * or define sensible values otherwise.
+ */
+
+ switch (dlme_el) {
+ case DLME_AT_EL1:
+ sctlr = read_sctlr_el1();
+ break;
+
+ case DLME_AT_EL2:
+ sctlr = read_sctlr_el2();
+ break;
+
+ default: /* Not reached */
+ ERROR("%s(): dlme_el has the unexpected value %d\n",
+ __func__, dlme_el);
+ panic();
+ }
+
+ sctlr &= ~(/* Disable DLME's EL MMU, since the existing page-tables are untrusted. */
+ SCTLR_M_BIT
+ | SCTLR_EE_BIT /* Little-endian data accesses. */
+ );
+
+ sctlr |= SCTLR_C_BIT | SCTLR_I_BIT; /* Allow instruction and data caching. */
+
+ switch (dlme_el) {
+ case DLME_AT_EL1:
+ write_sctlr_el1(sctlr);
+ break;
+
+ case DLME_AT_EL2:
+ write_sctlr_el2(sctlr);
+ break;
+ }
+}
+
+static void drtm_dl_reset_dlme_context(enum drtm_dlme_el dlme_el)
+{
+ void *ns_ctx = cm_get_context(NON_SECURE);
+ gp_regs_t *gpregs = get_gpregs_ctx(ns_ctx);
+ uint64_t spsr_el3 = read_ctx_reg(get_el3state_ctx(ns_ctx), CTX_SPSR_EL3);
+
+ /* Reset all gpregs, including SP_EL0. */
+ memset(gpregs, 0, sizeof(*gpregs));
+
+ /* Reset SP_ELx. */
+ switch (dlme_el) {
+ case DLME_AT_EL1:
+ write_sp_el1(0);
+ break;
+
+ case DLME_AT_EL2:
+ write_sp_el2(0);
+ break;
+ }
+
+ /*
+ * DLME's async exceptions are masked to avoid a NWd attacker's timed
+ * interference with any state we established trust in or measured.
+ */
+ spsr_el3 |= SPSR_DAIF_MASK << SPSR_DAIF_SHIFT;
+
+ write_ctx_reg(get_el3state_ctx(ns_ctx), CTX_SPSR_EL3, spsr_el3);
+}
+
+static void drtm_dl_prepare_eret_to_dlme(const struct_drtm_dl_args *args, enum drtm_dlme_el dlme_el)
+{
+ void *ctx = cm_get_context(NON_SECURE);
+ uint64_t dlme_ep = DL_ARGS_GET_DLME_ENTRY_POINT(args);
+ uint64_t spsr_el3 = read_ctx_reg(get_el3state_ctx(ctx), CTX_SPSR_EL3);
+
+ /* Next ERET is to the DLME's EL. */
+ spsr_el3 &= ~(MODE_EL_MASK << MODE_EL_SHIFT);
+ switch (dlme_el) {
+ case DLME_AT_EL1:
+ spsr_el3 |= MODE_EL1 << MODE_EL_SHIFT;
+ break;
+
+ case DLME_AT_EL2:
+ spsr_el3 |= MODE_EL2 << MODE_EL_SHIFT;
+ break;
+ }
+
+ /* Next ERET is to the DLME entry point. */
+ cm_set_elr_spsr_el3(NON_SECURE, dlme_ep, spsr_el3);
+}
+
static uint64_t drtm_dynamic_launch(uint64_t x1, void *handle)
{
enum drtm_retc ret = SUCCESS;
enum drtm_retc dma_prot_ret;
struct_drtm_dl_args args;
+ /* DLME should be highest NS exception level */
+ enum drtm_dlme_el dlme_el = (el_implemented(2) != EL_IMPL_NONE) ? MODE_EL2 : MODE_EL1;
/* Ensure that only boot PE is powered on */
ret = drtm_dl_check_cores();
@@ -499,7 +596,37 @@
goto err_undo_dma_prot;
}
+ /*
+ * Note that, at the time of writing, the DRTM spec allows a successful
+ * launch from NS-EL1 to return to a DLME in NS-EL2. The practical risk
+ * of a privilege escalation, e.g. due to a compromised hypervisor, is
+ * considered small enough not to warrant the specification of additional
+ * DRTM conduits that would be necessary to maintain OSs' abstraction from
+ * the presence of EL2 were the dynamic launch only be allowed from the
+ * highest NS EL.
+ */
+
+ dlme_el = (el_implemented(2) != EL_IMPL_NONE) ? MODE_EL2 : MODE_EL1;
+
+ drtm_dl_reset_dlme_el_state(dlme_el);
+ drtm_dl_reset_dlme_context(dlme_el);
+
+ /*
+ * TODO: Reset all SDEI event handlers, since they are untrusted. Both
+ * private and shared events for all cores must be unregistered.
+ * Note that simply calling SDEI ABIs would not be adequate for this, since
+ * there is currently no SDEI operation that clears private data for all PEs.
+ */
+
+ drtm_dl_prepare_eret_to_dlme(&args, dlme_el);
+
+ /*
+ * TODO: invalidate the instruction cache before jumping to the DLME.
+ * This is required to defend against potentially-malicious cache contents.
+ */
+
- SMC_RET1(handle, ret);
+ /* Return the DLME region's address in x0, and the DLME data offset in x1.*/
+ SMC_RET2(handle, args.dlme_paddr, args.dlme_data_off);
err_undo_dma_prot:
dma_prot_ret = drtm_dma_prot_disengage();
diff --git a/services/std_svc/drtm/drtm_main.h b/services/std_svc/drtm/drtm_main.h
index 230cbcf..baa37ae 100644
--- a/services/std_svc/drtm/drtm_main.h
+++ b/services/std_svc/drtm/drtm_main.h
@@ -36,6 +36,11 @@
#define DL_ARGS_GET_DLME_ENTRY_POINT(a) \
(((a)->dlme_paddr + (a)->dlme_img_off + (a)->dlme_img_ep_off))
+enum drtm_dlme_el {
+ DLME_AT_EL1 = MODE_EL1,
+ DLME_AT_EL2 = MODE_EL2
+};
+
enum drtm_retc {
SUCCESS = SMC_OK,
NOT_SUPPORTED = SMC_UNK,