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Date: Wed,  8 Jul 2020 23:03:15 -0500
From: "Christopher M. Riedl" <>
Subject: [PATCH v2 4/5] powerpc/lib: Add LKDTM accessor for patching addr

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 <>
 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..ffc6dfdbbf8e 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 */
+unsigned long read_cpu_patching_addr(unsigned int cpu);
diff --git a/arch/powerpc/lib/code-patching.c b/arch/powerpc/lib/code-patching.c
index 80fe3864f377..a12db2092947 100644
--- a/arch/powerpc/lib/code-patching.c
+++ b/arch/powerpc/lib/code-patching.c
@@ -51,6 +51,13 @@ int raw_patch_instruction(struct ppc_inst *addr, struct ppc_inst instr)
 static struct mm_struct *patching_mm __ro_after_init;
 static unsigned long patching_addr __ro_after_init;
+unsigned long read_cpu_patching_addr(unsigned int cpu)
+	return patching_addr;
 void __init poking_init(void)
 	spinlock_t *ptl; /* for protecting pte table */

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