[PATCH v4] arm: tcm: Don't crash when TCM banks are protected by TrustZone
Michael van der Westhuizen
michael at smart-africa.com
Thu Jun 4 04:58:41 PDT 2015
Fixes the TCM initialisation code to handle TCM banks that are
present but inaccessible due to TrustZone configuration. This is
the default case when enabling the non-secure world. It may also
be the case that that the user decided to use TCM for TrustZone.
This change has exposed a bug in handling of TCM where no TCM bank
was usable (the 0 size TCM case). This change addresses the
resulting hang.
This code only handles the ARMv6 TCMTR register format, and will not
work correctly on boards that use the ARMv7 (or any other) format.
This is handled by performing an early exit from the initialisation
function when the TCMTR reports any format other than v6.
Signed-off-by: Michael van der Westhuizen <michael at smart-africa.com>
Cc: Linus Walleij <linus.walleij at linaro.org>
Cc: Russell King <rmk+kernel at arm.linux.org.uk>
Cc: Dave Martin <Dave.Martin at arm.com>
---
Changes in v4:
- Clarify that the instruction encoding for unconditional MRC
happens to be identical between ARM and Thumb-2 modes.
Changes in v3:
- Add some documentation about the undefined handler hook and
how the values used in that hook are derived.
- Use symbolic values for the handler instruction and mask.
- Use symbolic values for the shift-and-mask operation that
extracts the destination register for the trapped operation.
- Reformat added comments to match the style in the remainder
of the file.
Changes in v2:
- Mark the TCM undefined hook data structure as __initdata, since
that's what it is.
- Ensure that we're dealing with an ARMv6 TCMTR format.
arch/arm/kernel/tcm.c | 104 ++++++++++++++++++++++++++++++++++++++++++++++++--
1 file changed, 101 insertions(+), 3 deletions(-)
diff --git a/arch/arm/kernel/tcm.c b/arch/arm/kernel/tcm.c
index 7a3be1d..b10e136 100644
--- a/arch/arm/kernel/tcm.c
+++ b/arch/arm/kernel/tcm.c
@@ -17,6 +17,9 @@
#include <asm/mach/map.h>
#include <asm/memory.h>
#include <asm/system_info.h>
+#include <asm/traps.h>
+
+#define TCMTR_FORMAT_MASK 0xe0000000U
static struct gen_pool *tcm_pool;
static bool dtcm_present;
@@ -176,6 +179,77 @@ static int __init setup_tcm_bank(u8 type, u8 bank, u8 banks,
}
/*
+ * When we are running in the non-secure world and the secure world
+ * has not explicitly given us access to the TCM we will get an
+ * undefined error when reading the TCM region register in the
+ * setup_tcm_bank function (above).
+ *
+ * There are two variants of this register read that we need to trap,
+ * the read for the data TCM and the read for the instruction TCM:
+ * c0370628: ee196f11 mrc 15, 0, r6, cr9, cr1, {0}
+ * c0370674: ee196f31 mrc 15, 0, r6, cr9, cr1, {1}
+ *
+ * Our undef hook mask explicitly matches all fields of the encoded
+ * instruction other than the destination register. The mask also
+ * only allows operand 2 to have the values 0 or 1.
+ *
+ * The undefined hook is defined as __init and __initdata, and therefore
+ * must be removed before tcm_init returns.
+ *
+ * In this particular case (MRC with ARM condition code ALways) the
+ * Thumb-2 and ARM instruction encoding are identical, so this hook
+ * will work on a Thumb-2 kernel.
+ *
+ * See A8.8.107, DDI0406C_C ARM Architecture Reference Manual, Encoding
+ * T1/A1 for the bit-by-bit details.
+ *
+ * mrc p15, 0, XX, c9, c1, 0
+ * mrc p15, 0, XX, c9, c1, 1
+ * | | | | | | | +---- opc2 0|1 = 000|001
+ * | | | | | | +------- CRm 0 = 0001
+ * | | | | | +----------- CRn 0 = 1001
+ * | | | | +--------------- Rt ? = ????
+ * | | | +------------------- opc1 0 = 000
+ * | | +----------------------- coproc 15 = 1111
+ * | +-------------------------- condition ALways = 1110
+ * +----------------------------- instruction MRC = 1110
+ *
+ * Encoding this as per A8.8.107 of DDI0406C, Encoding T1/A1, yields:
+ * 1111 1111 1111 1111 0000 1111 1101 1111 Required Mask
+ * 1110 1110 0001 1001 ???? 1111 0001 0001 mrc p15, 0, XX, c9, c1, 0
+ * 1110 1110 0001 1001 ???? 1111 0011 0001 mrc p15, 0, XX, c9, c1, 1
+ * [ ] [ ] [ ]| [ ] [ ] [ ] [ ]| +--- CRm
+ * | | | | | | | | +----- SBO
+ * | | | | | | | +------- opc2
+ * | | | | | | +----------- coproc
+ * | | | | | +---------------- Rt
+ * | | | | +--------------------- CRn
+ * | | | +------------------------- SBO
+ * | | +--------------------------- opc1
+ * | +------------------------------- instruction
+ * +------------------------------------ condition
+ */
+#define TCM_REGION_READ_MASK 0xffff0fdf
+#define TCM_REGION_READ_INSTR 0xee190f11
+#define DEST_REG_SHIFT 12
+#define DEST_REG_MASK 0xf
+
+static int __init tcm_handler(struct pt_regs *regs, unsigned int instr)
+{
+ regs->uregs[(instr >> DEST_REG_SHIFT) & DEST_REG_MASK] = 0;
+ regs->ARM_pc += 4;
+ return 0;
+}
+
+static struct undef_hook tcm_hook __initdata = {
+ .instr_mask = TCM_REGION_READ_MASK,
+ .instr_val = TCM_REGION_READ_INSTR,
+ .cpsr_mask = MODE_MASK,
+ .cpsr_val = SVC_MODE,
+ .fn = tcm_handler
+};
+
+/*
* This initializes the TCM memory
*/
void __init tcm_init(void)
@@ -204,9 +278,18 @@ void __init tcm_init(void)
}
tcm_status = read_cpuid_tcmstatus();
+
+ /*
+ * This code only supports v6-compatible TCMTR implementations.
+ */
+ if (tcm_status & TCMTR_FORMAT_MASK)
+ return;
+
dtcm_banks = (tcm_status >> 16) & 0x03;
itcm_banks = (tcm_status & 0x03);
+ register_undef_hook(&tcm_hook);
+
/* Values greater than 2 for D/ITCM banks are "reserved" */
if (dtcm_banks > 2)
dtcm_banks = 0;
@@ -218,7 +301,7 @@ void __init tcm_init(void)
for (i = 0; i < dtcm_banks; i++) {
ret = setup_tcm_bank(0, i, dtcm_banks, &dtcm_end);
if (ret)
- return;
+ goto unregister;
}
/* This means you compiled more code than fits into DTCM */
if (dtcm_code_sz > (dtcm_end - DTCM_OFFSET)) {
@@ -227,6 +310,12 @@ void __init tcm_init(void)
dtcm_code_sz, (dtcm_end - DTCM_OFFSET));
goto no_dtcm;
}
+ /*
+ * This means that the DTCM sizes were 0 or the DTCM banks
+ * were inaccessible due to TrustZone configuration.
+ */
+ if (!(dtcm_end - DTCM_OFFSET))
+ goto no_dtcm;
dtcm_res.end = dtcm_end - 1;
request_resource(&iomem_resource, &dtcm_res);
dtcm_iomap[0].length = dtcm_end - DTCM_OFFSET;
@@ -250,15 +339,21 @@ no_dtcm:
for (i = 0; i < itcm_banks; i++) {
ret = setup_tcm_bank(1, i, itcm_banks, &itcm_end);
if (ret)
- return;
+ goto unregister;
}
/* This means you compiled more code than fits into ITCM */
if (itcm_code_sz > (itcm_end - ITCM_OFFSET)) {
pr_info("CPU ITCM: %u bytes of code compiled to "
"ITCM but only %lu bytes of ITCM present\n",
itcm_code_sz, (itcm_end - ITCM_OFFSET));
- return;
+ goto unregister;
}
+ /*
+ * This means that the ITCM sizes were 0 or the ITCM banks
+ * were inaccessible due to TrustZone configuration.
+ */
+ if (!(itcm_end - ITCM_OFFSET))
+ goto unregister;
itcm_res.end = itcm_end - 1;
request_resource(&iomem_resource, &itcm_res);
itcm_iomap[0].length = itcm_end - ITCM_OFFSET;
@@ -275,6 +370,9 @@ no_dtcm:
pr_info("CPU ITCM: %u bytes of code compiled to ITCM but no "
"ITCM banks present in CPU\n", itcm_code_sz);
}
+
+unregister:
+ unregister_undef_hook(&tcm_hook);
}
/*
--
2.1.4
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