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

Jisheng Zhang
2022-12-04T18:00:11Z

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@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