Workaround for CVE-2017-5715 on Cortex A73 and A75
Invalidate the Branch Target Buffer (BTB) on entry to EL3 by
temporarily dropping into AArch32 Secure-EL1 and executing the
`BPIALL` instruction.
This is achieved by using 3 vector tables. There is the runtime
vector table which is used to handle exceptions and 2 additional
tables which are required to implement this workaround. The
additional tables are `vbar0` and `vbar1`.
The sequence of events for handling a single exception is
as follows:
1) Install vector table `vbar0` which saves the CPU context on entry
to EL3 and sets up the Secure-EL1 context to execute in AArch32 mode
with the MMU disabled and I$ enabled. This is the default vector table.
2) Before doing an ERET into Secure-EL1, switch vbar to point to
another vector table `vbar1`. This is required to restore EL3 state
when returning from the workaround, before proceeding with normal EL3
exception handling.
3) While in Secure-EL1, the `BPIALL` instruction is executed and an
SMC call back to EL3 is performed.
4) On entry to EL3 from Secure-EL1, the saved context from step 1) is
restored. The vbar is switched to point to `vbar0` in preparation to
handle further exceptions. Finally a branch to the runtime vector
table entry is taken to complete the handling of the original
exception.
This workaround is enabled by default on the affected CPUs.
NOTE
====
There are 4 different stubs in Secure-EL1. Each stub corresponds to
an exception type such as Sync/IRQ/FIQ/SError. Each stub will move a
different value in `R0` before doing an SMC call back into EL3.
Without this piece of information it would not be possible to know
what the original exception type was as we cannot use `ESR_EL3` to
distinguish between IRQs and FIQs.
Change-Id: I90b32d14a3735290b48685d43c70c99daaa4b434
Signed-off-by: Dimitris Papastamos <dimitris.papastamos@arm.com>
diff --git a/include/lib/aarch64/arch.h b/include/lib/aarch64/arch.h
index 96e2d5f..13a8c79 100644
--- a/include/lib/aarch64/arch.h
+++ b/include/lib/aarch64/arch.h
@@ -337,6 +337,11 @@
#define SPSR_T_ARM U(0x0)
#define SPSR_T_THUMB U(0x1)
+#define SPSR_M_SHIFT U(4)
+#define SPSR_M_MASK U(0x1)
+#define SPSR_M_AARCH64 U(0x0)
+#define SPSR_M_AARCH32 U(0x1)
+
#define DISABLE_ALL_EXCEPTIONS \
(DAIF_FIQ_BIT | DAIF_IRQ_BIT | DAIF_ABT_BIT | DAIF_DBG_BIT)
diff --git a/include/lib/el3_runtime/aarch64/context.h b/include/lib/el3_runtime/aarch64/context.h
index 5889904..5e212ec 100644
--- a/include/lib/el3_runtime/aarch64/context.h
+++ b/include/lib/el3_runtime/aarch64/context.h
@@ -46,12 +46,26 @@
#define CTX_GPREG_SP_EL0 U(0xf8)
#define CTX_GPREGS_END U(0x100)
+#if WORKAROUND_CVE_2017_5715
+#define CTX_CVE_2017_5715_OFFSET (CTX_GPREGS_OFFSET + CTX_GPREGS_END)
+#define CTX_CVE_2017_5715_QUAD0 U(0x0)
+#define CTX_CVE_2017_5715_QUAD1 U(0x8)
+#define CTX_CVE_2017_5715_QUAD2 U(0x10)
+#define CTX_CVE_2017_5715_QUAD3 U(0x18)
+#define CTX_CVE_2017_5715_QUAD4 U(0x20)
+#define CTX_CVE_2017_5715_QUAD5 U(0x28)
+#define CTX_CVE_2017_5715_END U(0x30)
+#else
+#define CTX_CVE_2017_5715_OFFSET CTX_GPREGS_OFFSET
+#define CTX_CVE_2017_5715_END CTX_GPREGS_END
+#endif
+
/*******************************************************************************
* Constants that allow assembler code to access members of and the 'el3_state'
* structure at their correct offsets. Note that some of the registers are only
* 32-bits wide but are stored as 64-bit values for convenience
******************************************************************************/
-#define CTX_EL3STATE_OFFSET (CTX_GPREGS_OFFSET + CTX_GPREGS_END)
+#define CTX_EL3STATE_OFFSET (CTX_CVE_2017_5715_OFFSET + CTX_CVE_2017_5715_END)
#define CTX_SCR_EL3 U(0x0)
#define CTX_RUNTIME_SP U(0x8)
#define CTX_SPSR_EL3 U(0x10)
@@ -186,6 +200,9 @@
/* Constants to determine the size of individual context structures */
#define CTX_GPREG_ALL (CTX_GPREGS_END >> DWORD_SHIFT)
+#if WORKAROUND_CVE_2017_5715
+#define CTX_CVE_2017_5715_ALL (CTX_CVE_2017_5715_END >> DWORD_SHIFT)
+#endif
#define CTX_SYSREG_ALL (CTX_SYSREGS_END >> DWORD_SHIFT)
#if CTX_INCLUDE_FPREGS
#define CTX_FPREG_ALL (CTX_FPREGS_END >> DWORD_SHIFT)
@@ -201,6 +218,10 @@
*/
DEFINE_REG_STRUCT(gp_regs, CTX_GPREG_ALL);
+#if WORKAROUND_CVE_2017_5715
+DEFINE_REG_STRUCT(cve_2017_5715_regs, CTX_CVE_2017_5715_ALL);
+#endif
+
/*
* AArch64 EL1 system register context structure for preserving the
* architectural state during switches from one security state to
@@ -242,6 +263,9 @@
*/
typedef struct cpu_context {
gp_regs_t gpregs_ctx;
+#if WORKAROUND_CVE_2017_5715
+ cve_2017_5715_regs_t cve_2017_5715_regs_ctx;
+#endif
el3_state_t el3state_ctx;
el1_sys_regs_t sysregs_ctx;
#if CTX_INCLUDE_FPREGS