[PATCH v2 10/13] RISC-V: fix auipc-jalr addresses in patched alternatives

Heiko Stuebner
2022-11-28T10:28:33Z

From: Heiko Stuebner <heiko.stuebner@vrull.eu>

Alternatives live in a different section, so addresses used by call
functions will point to wrong locations after the patch got applied.

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

Signed-off-by: Heiko Stuebner <heiko.stuebner@vrull.eu>
---
arch/riscv/include/asm/alternative.h | 3 ++
arch/riscv/kernel/alternative.c | 72 ++++++++++++++++++++++++++++
arch/riscv/kernel/cpufeature.c | 11 ++++-
3 files changed, 84 insertions(+), 2 deletions(-)

diff --git a/arch/riscv/include/asm/alternative.h b/arch/riscv/include/asm/alternative.h
index 6511dd73e812..c58ec3cc4bc3 100644
--- a/arch/riscv/include/asm/alternative.h
+++ b/arch/riscv/include/asm/alternative.h
@@ -27,6 +27,9 @@ void __init apply_boot_alternatives(void);
void __init apply_early_boot_alternatives(void);
void apply_module_alternatives(void *start, size_t length);

+void riscv_alternative_fix_auipc_jalr(void *alt_ptr, unsigned int len,
+ int patch_offset);
+
struct alt_entry {
void *old_ptr; /* address of original instruciton or data */
void *alt_ptr; /* address of replacement instruction or data */
diff --git a/arch/riscv/kernel/alternative.c b/arch/riscv/kernel/alternative.c
index a7d26a00beea..292cc42dc3be 100644
--- a/arch/riscv/kernel/alternative.c
+++ b/arch/riscv/kernel/alternative.c
@@ -15,6 +15,8 @@
#include <asm/vendorid_list.h>
#include <asm/sbi.h>
#include <asm/csr.h>
+#include <asm/insn.h>
+#include <asm/patch.h>

struct cpu_manufacturer_info_t {
unsigned long vendor_id;
@@ -53,6 +55,76 @@ static void __init_or_module riscv_fill_cpu_mfr_info(struct cpu_manufacturer_inf
}
}

+static unsigned int riscv_instruction_at(void *p, unsigned int offset)
+{
+ u16 *parcel = p + (offset * sizeof(u32));
+
+ return (unsigned int)parcel[0] | (unsigned int)parcel[1] << 16;
+}
+
+static inline bool riscv_insn_is_auipc_jalr(u32 insn1, u32 insn2)
+{
+ return riscv_insn_is_auipc(insn1) && riscv_insn_is_jalr(insn2);
+}
+
+#define JALR_SIGN_MASK BIT(RV_I_IMM_SIGN_OPOFF - RV_I_IMM_11_0_OPOFF)
+#define AUIPC_PAD (0x00001000)
+
+#define to_jalr_imm(value) \
+ ((value & RV_I_IMM_11_0_MASK) << RV_I_IMM_11_0_OPOFF)
+
+#define to_auipc_imm(value) \
+ ((value & JALR_SIGN_MASK) ? \
+ ((value & RV_U_IMM_31_12_MASK) + AUIPC_PAD) : \
+ (value & RV_U_IMM_31_12_MASK))
+
+void riscv_alternative_fix_auipc_jalr(void *alt_ptr, unsigned int len,
+ int patch_offset)
+{
+ int num_instr = len / sizeof(u32);
+ unsigned int call[2];
+ int i;
+ int imm;
+ u32 rd1;
+
+ /*
+ * stop one instruction before the end, as we're checking
+ * for auipc + jalr
+ */
+ for (i = 0; i < num_instr - 1; i++) {
+ u32 inst1 = riscv_instruction_at(alt_ptr, i);
+ u32 inst2 = riscv_instruction_at(alt_ptr, i + 1);
+
+ if (!riscv_insn_is_auipc_jalr(inst1, inst2))
+ continue;
+
+ /* call will use ra register */
+ rd1 = RV_EXTRACT_RD_REG(inst1);
+ if (rd1 != 1)
+ continue;
+
+ /* get and adjust new target address */
+ imm = RV_EXTRACT_UTYPE_IMM(inst1);
+ imm += RV_EXTRACT_ITYPE_IMM(inst2);
+ imm -= patch_offset;
+
+ /* pick the original auipc + jalr */
+ call[0] = inst1;
+ call[1] = inst2;
+
+ /* drop the old IMMs */
+ call[0] &= ~(RV_U_IMM_31_12_MASK);
+ call[1] &= ~(RV_I_IMM_11_0_MASK << RV_I_IMM_11_0_OPOFF);
+
+ /* add the adapted IMMs */
+ call[0] |= to_auipc_imm(imm);
+ call[1] |= to_jalr_imm(imm);
+
+ /* patch the call place again */
+ patch_text_nosync(alt_ptr + i * sizeof(u32), call, 8);
+ }
+}
+
/*
* 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 694267d1fe81..ba62a4ff5ccd 100644
--- a/arch/riscv/kernel/cpufeature.c
+++ b/arch/riscv/kernel/cpufeature.c
@@ -316,8 +316,15 @@ void __init_or_module riscv_cpufeature_patch_func(struct alt_entry *begin,
}

tmp = (1U << alt->errata_id);
- if (cpu_req_feature & tmp)
- patch_text_nosync(alt->old_ptr, alt->alt_ptr, alt->alt_len);
+ if (cpu_req_feature & tmp) {
+ /* do the basic patching */
+ patch_text_nosync(alt->old_ptr, alt->alt_ptr,
+ alt->alt_len);
+
+ riscv_alternative_fix_auipc_jalr(alt->old_ptr,
+ alt->alt_len,
+ alt->old_ptr - alt->alt_ptr);
+ }
}
}
#endif
--
2.35.1