[PATCH v2 01/13] riscv: fix jal offsets in patched alternatives

[Jisheng Zhang]

Alternatives live in a different section, so offsets used by jal
instruction will point to wrong locations after the patch got applied.

Similar to arm64, adjust the location to consider that offset.

Signed-off-by: Jisheng Zhang <jszhang at kernel.org>
---
 arch/riscv/include/asm/alternative.h |  2 ++
 arch/riscv/kernel/alternative.c      | 38 ++++++++++++++++++++++++++++
 arch/riscv/kernel/cpufeature.c       |  3 +++
 3 files changed, 43 insertions(+)

diff --git a/arch/riscv/include/asm/alternative.h b/arch/riscv/include/asm/alternative.h
index c58ec3cc4bc3..33eae9541684 100644
--- a/arch/riscv/include/asm/alternative.h
+++ b/arch/riscv/include/asm/alternative.h
@@ -29,6 +29,8 @@ void apply_module_alternatives(void *start, size_t length);
 
 void riscv_alternative_fix_auipc_jalr(void *alt_ptr, unsigned int len,
 				      int patch_offset);
+void riscv_alternative_fix_jal(void *alt_ptr, unsigned int len,
+			       int patch_offset);
 
 struct alt_entry {
 	void *old_ptr;		 /* address of original instruciton or data  */
diff --git a/arch/riscv/kernel/alternative.c b/arch/riscv/kernel/alternative.c
index 292cc42dc3be..9d88375624b5 100644
--- a/arch/riscv/kernel/alternative.c
+++ b/arch/riscv/kernel/alternative.c
@@ -125,6 +125,44 @@ void riscv_alternative_fix_auipc_jalr(void *alt_ptr, unsigned int len,
 	}
 }
 
+#define to_jal_imm(value)						\
+	(((value & (RV_J_IMM_10_1_MASK << RV_J_IMM_10_1_OFF)) << RV_I_IMM_11_0_OPOFF) | \
+	 ((value & (RV_J_IMM_11_MASK << RV_J_IMM_11_OFF)) << RV_J_IMM_11_OPOFF) | \
+	 ((value & (RV_J_IMM_19_12_OPOFF << RV_J_IMM_19_12_OFF)) << RV_J_IMM_19_12_OPOFF) | \
+	 ((value & (1 << RV_J_IMM_SIGN_OFF)) << RV_J_IMM_SIGN_OPOFF))
+
+void riscv_alternative_fix_jal(void *alt_ptr, unsigned int len,
+			       int patch_offset)
+{
+	int num_instr = len / sizeof(u32);
+	unsigned int call;
+	int i;
+	int imm;
+
+	for (i = 0; i < num_instr; i++) {
+		u32 inst = riscv_instruction_at(alt_ptr, i);
+
+		if (!riscv_insn_is_jal(inst))
+			continue;
+
+		/* get and adjust new target address */
+		imm = RV_EXTRACT_JTYPE_IMM(inst);
+		imm -= patch_offset;
+
+		/* pick the original jal */
+		call = inst;
+
+		/* drop the old IMMs, all jal imm bits sit at 31:12 */
+		call &= ~GENMASK(31, 12);
+
+		/* add the adapted IMMs */
+		call |= to_jal_imm(imm);
+
+		/* patch the call place again */
+		patch_text_nosync(alt_ptr + i * sizeof(u32), &call, 4);
+	}
+}
+
 /*
  * This is called very early in the boot process (directly after we run
  * a feature detect on the boot CPU). No need to worry about other CPUs
diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
index ba62a4ff5ccd..c743f0adc794 100644
--- a/arch/riscv/kernel/cpufeature.c
+++ b/arch/riscv/kernel/cpufeature.c
@@ -324,6 +324,9 @@ void __init_or_module riscv_cpufeature_patch_func(struct alt_entry *begin,
 			riscv_alternative_fix_auipc_jalr(alt->old_ptr,
 							 alt->alt_len,
 							 alt->old_ptr - alt->alt_ptr);
+			riscv_alternative_fix_jal(alt->old_ptr,
+						  alt->alt_len,
+						  alt->old_ptr - alt->alt_ptr);
 		}
 	}
 }
-- 
2.37.2