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Subject[PATCH] riscv: blacklist assembly symbols for kprobe
Date
Adding kprobes on some assembly functions (mainly exception handling)
will result in crashes (either recursive trap or panic). To avoid such
errors, add ASM_NOKPROBE() macro which allow adding specific symbols
into the __kprobe_blacklist section and use to blacklist the following
symbols that showed to be problematic:
- handle_exception()
- ret_from_exception()
- handle_kernel_stack_overflow()

Signed-off-by: Clément Léger <cleger@rivosinc.com>
---
arch/riscv/include/asm/asm.h | 10 ++++++++++
arch/riscv/kernel/entry.S | 3 +++
2 files changed, 13 insertions(+)

diff --git a/arch/riscv/include/asm/asm.h b/arch/riscv/include/asm/asm.h
index 114bbadaef41..9194e334de15 100644
--- a/arch/riscv/include/asm/asm.h
+++ b/arch/riscv/include/asm/asm.h
@@ -142,6 +142,16 @@
REG_L x31, PT_T6(sp)
.endm

+/* Annotate a function as being unsuitable for kprobes. */
+#ifdef CONFIG_KPROBES
+#define ASM_NOKPROBE(name) \
+ .pushsection "_kprobe_blacklist", "aw"; \
+ RISCV_PTR name; \
+ .popsection
+#else
+#define ASM_NOKPROBE(name)
+#endif
+
#endif /* __ASSEMBLY__ */

#endif /* _ASM_RISCV_ASM_H */
diff --git a/arch/riscv/kernel/entry.S b/arch/riscv/kernel/entry.S
index 143a2bb3e697..f24bc4eeedde 100644
--- a/arch/riscv/kernel/entry.S
+++ b/arch/riscv/kernel/entry.S
@@ -101,6 +101,7 @@ _save_context:
1:
tail do_trap_unknown
SYM_CODE_END(handle_exception)
+ASM_NOKPROBE(handle_exception)

/*
* The ret_from_exception must be called with interrupt disabled. Here is the
@@ -167,6 +168,7 @@ SYM_CODE_START_NOALIGN(ret_from_exception)
sret
#endif
SYM_CODE_END(ret_from_exception)
+ASM_NOKPROBE(ret_from_exception)

#ifdef CONFIG_VMAP_STACK
SYM_CODE_START_LOCAL(handle_kernel_stack_overflow)
@@ -254,6 +256,7 @@ restore_caller_reg:
move a0, sp
tail handle_bad_stack
SYM_CODE_END(handle_kernel_stack_overflow)
+ASM_NOKPROBE(handle_kernel_stack_overflow)
#endif

SYM_CODE_START(ret_from_fork)
--
2.42.0
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