runtime_exceptions: Update AT speculative workaround
As per latest mailing communication [1], we decided to
update AT speculative workaround implementation in order to
disable page table walk for lower ELs(EL1 or EL0) immediately
after context switching to EL3 from lower ELs.
Previous implementation of AT speculative workaround is available
here: 45aecff00
AT speculative workaround is updated as below:
1. Avoid saving and restoring of SCTLR and TCR registers for EL1
in context save and restore routine respectively.
2. On EL3 entry, save SCTLR and TCR registers for EL1.
3. On EL3 entry, update EL1 system registers to disable stage 1
page table walk for lower ELs (EL1 and EL0) and enable EL1
MMU.
4. On EL3 exit, restore SCTLR and TCR registers for EL1 which
are saved in step 2.
[1]:
https://lists.trustedfirmware.org/pipermail/tf-a/2020-July/000586.html
Change-Id: Iee8de16f81dc970a8f492726f2ddd57e7bd9ffb5
Signed-off-by: Manish V Badarkhe <Manish.Badarkhe@arm.com>
diff --git a/lib/el3_runtime/aarch64/context.S b/lib/el3_runtime/aarch64/context.S
index 12e5d49..1cb527d 100644
--- a/lib/el3_runtime/aarch64/context.S
+++ b/lib/el3_runtime/aarch64/context.S
@@ -8,6 +8,7 @@
#include <asm_macros.S>
#include <assert_macros.S>
#include <context.h>
+#include <el3_common_macros.S>
#if CTX_INCLUDE_EL2_REGS
.global el2_sysregs_context_save
@@ -22,6 +23,7 @@
#endif
.global save_gp_pmcr_pauth_regs
.global restore_gp_pmcr_pauth_regs
+ .global save_and_update_ptw_el1_sys_regs
.global el3_exit
#if CTX_INCLUDE_EL2_REGS
@@ -420,9 +422,11 @@
mrs x10, elr_el1
stp x9, x10, [x0, #CTX_SPSR_EL1]
+#if !ERRATA_SPECULATIVE_AT
mrs x15, sctlr_el1
mrs x16, tcr_el1
stp x15, x16, [x0, #CTX_SCTLR_EL1]
+#endif
mrs x17, cpacr_el1
mrs x9, csselr_el1
@@ -517,9 +521,11 @@
msr spsr_el1, x9
msr elr_el1, x10
+#if !ERRATA_SPECULATIVE_AT
ldp x15, x16, [x0, #CTX_SCTLR_EL1]
msr sctlr_el1, x15
msr tcr_el1, x16
+#endif
ldp x17, x9, [x0, #CTX_CPACR_EL1]
msr cpacr_el1, x17
@@ -859,6 +865,48 @@
ret
endfunc restore_gp_pmcr_pauth_regs
+/*
+ * In case of ERRATA_SPECULATIVE_AT, save SCTLR_EL1 and TCR_EL1
+ * registers and update EL1 registers to disable stage1 and stage2
+ * page table walk
+ */
+func save_and_update_ptw_el1_sys_regs
+ /* ----------------------------------------------------------
+ * Save only sctlr_el1 and tcr_el1 registers
+ * ----------------------------------------------------------
+ */
+ mrs x29, sctlr_el1
+ str x29, [sp, #(CTX_EL1_SYSREGS_OFFSET + CTX_SCTLR_EL1)]
+ mrs x29, tcr_el1
+ str x29, [sp, #(CTX_EL1_SYSREGS_OFFSET + CTX_TCR_EL1)]
+
+ /* ------------------------------------------------------------
+ * Must follow below order in order to disable page table
+ * walk for lower ELs (EL1 and EL0). First step ensures that
+ * page table walk is disabled for stage1 and second step
+ * ensures that page table walker should use TCR_EL1.EPDx
+ * bits to perform address translation. ISB ensures that CPU
+ * does these 2 steps in order.
+ *
+ * 1. Update TCR_EL1.EPDx bits to disable page table walk by
+ * stage1.
+ * 2. Enable MMU bit to avoid identity mapping via stage2
+ * and force TCR_EL1.EPDx to be used by the page table
+ * walker.
+ * ------------------------------------------------------------
+ */
+ orr x29, x29, #(TCR_EPD0_BIT)
+ orr x29, x29, #(TCR_EPD1_BIT)
+ msr tcr_el1, x29
+ isb
+ mrs x29, sctlr_el1
+ orr x29, x29, #SCTLR_M_BIT
+ msr sctlr_el1, x29
+ isb
+
+ ret
+endfunc save_and_update_ptw_el1_sys_regs
+
/* ------------------------------------------------------------------
* This routine assumes that the SP_EL3 is pointing to a valid
* context structure from where the gp regs and other special
@@ -903,6 +951,8 @@
blr x17
1:
#endif
+ restore_ptw_el1_sys_regs
+
/* ----------------------------------------------------------
* Restore general purpose (including x30), PMCR_EL0 and
* ARMv8.3-PAuth registers.