* [PATCH] gdb/arm: Fix M-profile EXC_RETURN exception_domain_is_secure logic
@ 2022-10-22 7:58 Tomas Vanek
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From: Tomas Vanek @ 2022-10-22 7:58 UTC (permalink / raw)
To: gdb-patches
Arm v8-M Architecture Reference Manual,
D1.2.95 EXC_RETURN, Exception Return Payload
describes ES bit:
"ES, bit [0]
Exception Secure. The security domain the exception was taken to.
The possible values of this bit are:
0 Non-secure.
1 Secure"
arm-tdep.c:3443, arm_m_exception_cache () function tests this bit:
exception_domain_is_secure = (bit (lr, 0) == 0);
The test is negated!
Later on line 3553, the condition evaluates if an additional state
context is stacked:
/* With the Security extension, the hardware saves R4..R11 too. */
if (tdep->have_sec_ext && secure_stack_used
&& (!default_callee_register_stacking || exception_domain_is_secure))
RM, B3.19 Exception entry, context stacking
reads:
RPLHM "In a PE with the Security Extension, on taking an exception,
the PE hardware:
...
2. If exception entry requires a transition from Secure state to
Non-secure state, the PE hardware extends the stack frame and also
saves additional state context."
So we should test for !exception_domain_is_secure instead of non-negated
value!
These two bugs compensate each other so unstacking works correctly.
But another test of exception_domain_is_secure (negated due to the
first bug) prevents arm_unwind_secure_frames to work as expected:
/* Unwinding from non-secure to secure can trip security
measures. In order to avoid the debugger being
intrusive, rely on the user to configure the requested
mode. */
if (secure_stack_used && !exception_domain_is_secure
&& !arm_unwind_secure_frames)
Test with GNU gdb (GDB) 13.0.50.20221016-git.
Stopped in a non-secure handler:
(gdb) set arm unwind-secure-frames 0
(gdb) bt
at C:/dvl/stm32l5trustzone/GPIO_IOToggle_TrustZone/NonSecure/Src/nsstm32l5xx_it.c:134
at C:/dvl/stm32l5trustzone/GPIO_IOToggle_TrustZone/Drivers/STM32L5xx_HAL_Driver/Src/stm32l5xx_hal_gpio.c:386
Backtrace stopped: previous frame inner to this frame (corrupt stack?)
The frames #3 and #4 are secure. backtrace should stop before #3.
Stopped in a secure handler:
(gdb) bt
at C:/dvl/stm32l5trustzone/GPIO_IOToggle_TrustZone/Secure/Src/stm32l5xx_it.c:234
warning: Non-secure to secure stack unwinding disabled.
The exception from secure to secure erroneously stops unwinding. It should
continue as far as the security unlimited backtrace:
(gdb) set arm unwind-secure-frames 1
(gdb) si <-- used to rebuild frame cache after change of unwind-secure-frames
0x0c0008e6 425 if (SecureTimingDelay != 0U)
(gdb) bt
at C:/dvl/stm32l5trustzone/GPIO_IOToggle_TrustZone/Secure/Src/stm32l5xx_it.c:234
Backtrace stopped: previous frame inner to this frame (corrupt stack?)
Set exception_domain_is_secure to the value expected by its name.
Fix exception_domain_is_secure usage in the additional state context
stacking condition.
Signed-off-by: Tomas Vanek <vanekt@fbl.cz>
---
gdb/arm-tdep.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/gdb/arm-tdep.c b/gdb/arm-tdep.c
index 55295e1..20b6f3f 100644
--- a/gdb/arm-tdep.c
+++ b/gdb/arm-tdep.c
@@ -3496,7 +3496,7 @@ struct frame_unwind arm_stub_unwind = {
{
secure_stack_used = (bit (lr, 6) != 0);
default_callee_register_stacking = (bit (lr, 5) != 0);
- exception_domain_is_secure = (bit (lr, 0) == 0);
+ exception_domain_is_secure = (bit (lr, 0) != 0);
/* Unwinding from non-secure to secure can trip security
measures. In order to avoid the debugger being
@@ -3606,7 +3606,7 @@ struct frame_unwind arm_stub_unwind = {
/* With the Security extension, the hardware saves R4..R11 too. */
if (tdep->have_sec_ext && secure_stack_used
- && (!default_callee_register_stacking || exception_domain_is_secure))
+ && (!default_callee_register_stacking || !exception_domain_is_secure))
{
/* Read R4..R11 from the integer callee registers. */
cache->saved_regs[4].set_addr (unwound_sp + 0x08);
--
1.9.1
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