Subject: [PATCH v3 1/6] powerpc: Add LKDTM accessor for patching addr

From: "Christopher M. Riedl" <[email-masked]>
Date: Thu, 27 Aug 2020 00:26:54 -0500

When live patching a STRICT_RWX kernel, a mapping is installed at a
"patching address" with temporary write permissions. Provide a
LKDTM-only accessor function for this address in preparation for a LKDTM
test which attempts to "hijack" this mapping by writing to it from
another CPU.

Signed-off-by: Christopher M. Riedl <[email-masked]>
---
 arch/powerpc/include/asm/code-patching.h | 4 ++++
 arch/powerpc/lib/code-patching.c         | 7 +++++++
 2 files changed, 11 insertions(+)

diff --git a/arch/powerpc/include/asm/code-patching.h b/arch/powerpc/include/asm/code-patching.h
index eacc9102c251..7216d6a6bb0a 100644
--- a/arch/powerpc/include/asm/code-patching.h
+++ b/arch/powerpc/include/asm/code-patching.h
@@ -187,4 +187,8 @@ static inline unsigned long ppc_kallsyms_lookup_name(const char *name)
 				 ___PPC_RA(__REG_R1) | PPC_LR_STKOFF)
 #endif /* CONFIG_PPC64 */
 
+#if defined(CONFIG_LKDTM) && defined(CONFIG_STRICT_KERNEL_RWX)
+unsigned long read_cpu_patching_addr(unsigned int cpu);
+#endif
+
 #endif /* _ASM_POWERPC_CODE_PATCHING_H */
diff --git a/arch/powerpc/lib/code-patching.c b/arch/powerpc/lib/code-patching.c
index 8c3934ea6220..85d3fdca9452 100644
--- a/arch/powerpc/lib/code-patching.c
+++ b/arch/powerpc/lib/code-patching.c
@@ -46,6 +46,13 @@ int raw_patch_instruction(struct ppc_inst *addr, struct ppc_inst instr)
 #ifdef CONFIG_STRICT_KERNEL_RWX
 static DEFINE_PER_CPU(struct vm_struct *, text_poke_area);
 
+#ifdef CONFIG_LKDTM
+unsigned long read_cpu_patching_addr(unsigned int cpu)
+{
+	return (unsigned long)(per_cpu(text_poke_area, cpu))->addr;
+}
+#endif
+
 static int text_area_cpu_up(unsigned int cpu)
 {
 	struct vm_struct *area;
-- 
2.28.0