cpus: denver: Implement static workaround for CVE-2018-3639

For Denver CPUs, this approach enables the mitigation during EL3
initialization, following every PE reset. No mechanism is provided to
disable the mitigation at runtime.

This approach permanently mitigates the EL3 software stack only. Other
software components are responsible to enable it for their exception
levels.

TF-A implements this approach for the Denver CPUs with DENVER_MIDR_PN3
and earlier:

*   By setting bit 11 (Disable speculative store buffering) of
    `ACTLR_EL3`

*   By setting bit 9 (Disable speculative memory disambiguation) of
    `ACTLR_EL3`

TF-A implements this approach for the Denver CPUs with DENVER_MIDR_PN4
and later:

*   By setting bit 18 (Disable speculative store buffering) of
    `ACTLR_EL3`

*   By setting bit 17 (Disable speculative memory disambiguation) of
    `ACTLR_EL3`

Change-Id: If1de96605ce3f7b0aff5fab2c828e5aecb687555
Signed-off-by: Varun Wadekar <vwadekar@nvidia.com>

include/lib/cpus/aarch64/denver.h

@@ -20,6 +20,14 @@
 /* CPU state ids - implementation defined */
 #define DENVER_CPU_STATE_POWER_DOWN	U(0x3)
 
+/* Speculative store buffering */
+#define DENVER_CPU_DIS_SSB_EL3		(U(1) << 11)
+#define DENVER_PN4_CPU_DIS_SSB_EL3	(U(1) << 18)
+
+/* Speculative memory disambiguation */
+#define DENVER_CPU_DIS_MD_EL3		(U(1) << 9)
+#define DENVER_PN4_CPU_DIS_MD_EL3	(U(1) << 17)
+
 /* Core power management states */
 #define DENVER_CPU_PMSTATE_C1		U(0x1)
 #define DENVER_CPU_PMSTATE_C6		U(0x6)

lib/cpus/aarch64/denver.S

@@ -211,6 +211,15 @@ func check_errata_cve_2017_5715
 	ret
 endfunc check_errata_cve_2017_5715
 
+func check_errata_cve_2018_3639
+#if WORKAROUND_CVE_2018_3639
+	mov	x0, #ERRATA_APPLIES
+#else
+	mov	x0, #ERRATA_MISSING
+#endif
+	ret
+endfunc check_errata_cve_2018_3639
+
 	/* -------------------------------------------------
 	 * The CPU Ops reset function for Denver.
 	 * -------------------------------------------------
@@ -236,6 +245,25 @@ func denver_reset_func
 	msr	vbar_el3, x0
 #endif
 
+#if WORKAROUND_CVE_2018_3639
+	/*
+	 * Denver CPUs with DENVER_MIDR_PN3 or earlier, use different
+	 * bits in the ACTLR_EL3 register to disable speculative
+	 * store buffer and memory disambiguation.
+	 */
+	mrs	x0, midr_el1
+	mov_imm	x1, DENVER_MIDR_PN4
+	cmp	x0, x1
+	mrs	x0, actlr_el3
+	mov	x1, #(DENVER_CPU_DIS_MD_EL3 | DENVER_CPU_DIS_SSB_EL3)
+	mov	x2, #(DENVER_PN4_CPU_DIS_MD_EL3 | DENVER_PN4_CPU_DIS_SSB_EL3)
+	csel	x3, x1, x2, ne
+	orr	x0, x0, x3
+	msr	actlr_el3, x0
+	isb
+	dsb	sy
+#endif
+
 	/* ----------------------------------------------------
 	 * Reset ACTLR.PMSTATE to C1 state
 	 * ----------------------------------------------------
@@ -294,6 +322,7 @@ func denver_errata_report
 	 * checking functions of each errata.
 	 */
 	report_errata WORKAROUND_CVE_2017_5715, denver, cve_2017_5715
+	report_errata WORKAROUND_CVE_2018_3639, denver, cve_2018_3639
 
 	ldp	x8, x30, [sp], #16
 	ret