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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [xen master] xen/arm: arm64: Add emulation of Debug Data Transfer Registers
commit 43c416d0d81957229b5b5d73be694fb1ba149a3e
Author: Michal Orzel <michal.orzel@xxxxxxx>
AuthorDate: Thu Mar 7 12:39:42 2024 +0000
Commit: Julien Grall <jgrall@xxxxxxxxxx>
CommitDate: Thu Mar 14 13:04:25 2024 +0000
xen/arm: arm64: Add emulation of Debug Data Transfer Registers
Currently, if user enables HVC_DCC config option in Linux, it invokes access
to debug data transfer registers (i.e. DBGDTRTX_EL0 on arm64, DBGDTRTXINT on
arm32). As these registers are not emulated, Xen injects an undefined
exception to the guest and Linux crashes.
To prevent this crash, introduce a partial emulation of DBGDTR[TR]X_EL0
(these registers share the same encoding) as RAZ/WI and MDCCSR_EL0 as
TXfull.
Refer ARM DDI 0487J.a ID042523, D19.3.8, DBGDTRTX_EL0
"If TXfull is set to 1, set DTRRX and DTRTX to UNKNOWN".
Thus, any OS is expected to read MDCCSR_EL0 and check for TXfull before
using DBGDTRTX_EL0. Linux does it via hvc_dcc_init() ---> hvc_dcc_check(),
and returns -ENODEV in case TXfull bit is still set after writing a test
character. This way we prevent the guest from making use of HVC DCC as a
console.
Signed-off-by: Michal Orzel <michal.orzel@xxxxxxx>
Signed-off-by: Ayan Kumar Halder <ayan.kumar.halder@xxxxxxx>
Acked-by: Julien Grall <jgrall@xxxxxxxxxx>
---
SUPPORT.md | 5 +++
xen/arch/arm/arm64/vsysreg.c | 69 +++++++++++++++++++++++++-----------
xen/arch/arm/include/asm/arm64/hsr.h | 3 ++
3 files changed, 56 insertions(+), 21 deletions(-)
diff --git a/SUPPORT.md b/SUPPORT.md
index ad74f5a329..465f6527c9 100644
--- a/SUPPORT.md
+++ b/SUPPORT.md
@@ -111,6 +111,11 @@ that would normally trigger a fault injection.
Only the following system registers are security supported:
+ MDCCSR_EL0
+ DBGDTR_EL0
+ DBGDTRTX_EL0
+ DBGDTRRX_EL0
+
### ARM Scalable Vector Extension (SVE/SVE2)
Arm64 domains can use Scalable Vector Extension (SVE/SVE2).
diff --git a/xen/arch/arm/arm64/vsysreg.c b/xen/arch/arm/arm64/vsysreg.c
index b5d54c569b..c73b2c95ce 100644
--- a/xen/arch/arm/arm64/vsysreg.c
+++ b/xen/arch/arm/arm64/vsysreg.c
@@ -82,6 +82,7 @@ TVM_REG(CONTEXTIDR_EL1)
void do_sysreg(struct cpu_user_regs *regs,
const union hsr hsr)
{
+ const struct hsr_sysreg sysreg = hsr.sysreg;
int regidx = hsr.sysreg.reg;
struct vcpu *v = current;
@@ -159,9 +160,6 @@ void do_sysreg(struct cpu_user_regs *regs,
*
* Unhandled:
* MDCCINT_EL1
- * DBGDTR_EL0
- * DBGDTRRX_EL0
- * DBGDTRTX_EL0
* OSDTRRX_EL1
* OSDTRTX_EL1
* OSECCR_EL1
@@ -171,12 +169,42 @@ void do_sysreg(struct cpu_user_regs *regs,
*/
case HSR_SYSREG_MDSCR_EL1:
return handle_raz_wi(regs, regidx, hsr.sysreg.read, hsr, 1);
+
+ /*
+ * Xen doesn't expose a real (or emulated) Debug Communications Channel
+ * (DCC) to a domain. Yet the Arm ARM implies this is not an optional
+ * feature. So some domains may start to probe it. For instance, the
+ * HVC_DCC driver in Linux (since f377775dc083 and at least up to v6.7),
+ * will try to write some characters and check if the transmit buffer
+ * has emptied.
+ */
case HSR_SYSREG_MDCCSR_EL0:
/*
+ * By setting TX status bit (only if partial emulation is enabled) to
+ * indicate the transmit buffer is full, we would hint the OS that the
+ * DCC is probably not working.
+ *
+ * Bit 29: TX full
+ *
* Accessible at EL0 only if MDSCR_EL1.TDCC is set to 0. We emulate
that
* register as RAZ/WI above. So RO at both EL0 and EL1.
*/
- return handle_ro_raz(regs, regidx, hsr.sysreg.read, hsr, 0);
+ return handle_ro_read_val(regs, regidx, hsr.sysreg.read, hsr, 0,
+ partial_emulation ? (1U << 29) : 0);
+
+ case HSR_SYSREG_DBGDTR_EL0:
+ /* DBGDTR[TR]X_EL0 share the same encoding */
+ case HSR_SYSREG_DBGDTRTX_EL0:
+ /*
+ * Emulate as RAZ/WI (only if partial emulation is enabled) to prevent
+ * injecting undefined exception.
+ * Accessible at EL0 only if MDSCR_EL1.TDCC is set to 0. We emulate
that
+ * register as RAZ/WI.
+ */
+ if ( !partial_emulation )
+ goto fail;
+ return handle_raz_wi(regs, regidx, hsr.sysreg.read, hsr, 0);
+
HSR_SYSREG_DBG_CASES(DBGBVR):
HSR_SYSREG_DBG_CASES(DBGBCR):
HSR_SYSREG_DBG_CASES(DBGWVR):
@@ -394,26 +422,25 @@ void do_sysreg(struct cpu_user_regs *regs,
* And all other unknown registers.
*/
default:
- {
- const struct hsr_sysreg sysreg = hsr.sysreg;
-
- gdprintk(XENLOG_ERR,
- "%s %d, %d, c%d, c%d, %d %s x%d @ 0x%"PRIregister"\n",
- sysreg.read ? "mrs" : "msr",
- sysreg.op0, sysreg.op1,
- sysreg.crn, sysreg.crm,
- sysreg.op2,
- sysreg.read ? "=>" : "<=",
- sysreg.reg, regs->pc);
- gdprintk(XENLOG_ERR,
- "unhandled 64-bit sysreg access %#"PRIregister"\n",
- hsr.bits & HSR_SYSREG_REGS_MASK);
- inject_undef_exception(regs, hsr);
- return;
- }
+ goto fail;
}
regs->pc += 4;
+ return;
+
+ fail:
+ gdprintk(XENLOG_ERR,
+ "%s %d, %d, c%d, c%d, %d %s x%d @ 0x%"PRIregister"\n",
+ sysreg.read ? "mrs" : "msr",
+ sysreg.op0, sysreg.op1,
+ sysreg.crn, sysreg.crm,
+ sysreg.op2,
+ sysreg.read ? "=>" : "<=",
+ sysreg.reg, regs->pc);
+ gdprintk(XENLOG_ERR,
+ "unhandled 64-bit sysreg access %#"PRIregister"\n",
+ hsr.bits & HSR_SYSREG_REGS_MASK);
+ inject_undef_exception(regs, hsr);
}
/*
diff --git a/xen/arch/arm/include/asm/arm64/hsr.h
b/xen/arch/arm/include/asm/arm64/hsr.h
index e691d41c17..1495ccddea 100644
--- a/xen/arch/arm/include/asm/arm64/hsr.h
+++ b/xen/arch/arm/include/asm/arm64/hsr.h
@@ -47,6 +47,9 @@
#define HSR_SYSREG_OSDLR_EL1 HSR_SYSREG(2,0,c1,c3,4)
#define HSR_SYSREG_DBGPRCR_EL1 HSR_SYSREG(2,0,c1,c4,4)
#define HSR_SYSREG_MDCCSR_EL0 HSR_SYSREG(2,3,c0,c1,0)
+#define HSR_SYSREG_DBGDTR_EL0 HSR_SYSREG(2,3,c0,c4,0)
+#define HSR_SYSREG_DBGDTRTX_EL0 HSR_SYSREG(2,3,c0,c5,0)
+#define HSR_SYSREG_DBGDTRRX_EL0 HSR_SYSREG(2,3,c0,c5,0)
#define HSR_SYSREG_DBGBVRn_EL1(n) HSR_SYSREG(2,0,c0,c##n,4)
#define HSR_SYSREG_DBGBCRn_EL1(n) HSR_SYSREG(2,0,c0,c##n,5)
--
generated by git-patchbot for /home/xen/git/xen.git#master
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