riscv: fix jal offsets in patched alternatives

Commit Message

Heiko Stübner Jan. 13, 2023, 9:22 p.m. UTC

From: Jisheng Zhang <[e-mail]>

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.

Co-developed-by: Heiko Stuebner <[e-mail]>
Signed-off-by: Jisheng Zhang <[e-mail]>
Reviewed-by: Conor Dooley <[e-mail]>
Reviewed-by: Andrew Jones <[e-mail]>
Signed-off-by: Heiko Stuebner <[e-mail]>
---
This is exactly the same patch, that Jisheng sent as part of his
isa-extension series [0], just split out into a separate patch,
as at least two series depend on it.

[0] https://lore.kernel.org/r/[e-mail]

 arch/riscv/include/asm/insn.h   | 27 +++++++++++++++++++++++++++
 arch/riscv/kernel/alternative.c | 27 +++++++++++++++++++++++++++
 2 files changed, 54 insertions(+)

Comments

Palmer Dabbelt Jan. 25, 2023, 3:48 a.m. UTC | #1

On Fri, 13 Jan 2023 22:22:05 +0100, Heiko Stuebner wrote:
> From: Jisheng Zhang <[e-mail]>
> 
> 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.
> 
> [...]

Applied, thanks!

[1/1] riscv: fix jal offsets in patched alternatives
      https://git.kernel.org/palmer/c/9d5567ccf96f

Best regards,

[e-mail] Jan. 25, 2023, 3:50 a.m. UTC | #2

Hello:

This patch was applied to riscv/linux.git (for-next)
by Palmer Dabbelt <[e-mail]>:

On Fri, 13 Jan 2023 22:22:05 +0100 you wrote:
> From: Jisheng Zhang <[e-mail]>
> 
> 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.
> 
> [...]

Here is the summary with links:
  - riscv: fix jal offsets in patched alternatives
    https://git.kernel.org/riscv/c/9d5567ccf96f

You are awesome, thank you!

Patch

diff --git a/arch/riscv/include/asm/insn.h b/arch/riscv/include/asm/insn.h
index 98453535324a..1d2df245d0bd 100644
--- a/arch/riscv/include/asm/insn.h
+++ b/arch/riscv/include/asm/insn.h
@@ -291,6 +291,33 @@  static __always_inline bool riscv_insn_is_branch(u32 code)
 	(RVC_X(x_, RVC_B_IMM_7_6_OPOFF, RVC_B_IMM_7_6_MASK) << RVC_B_IMM_7_6_OFF) | \
 	(RVC_IMM_SIGN(x_) << RVC_B_IMM_SIGN_OFF); })
 
+/*
+ * Get the immediate from a J-type instruction.
+ *
+ * @insn: instruction to process
+ * Return: immediate
+ */
+static inline s32 riscv_insn_extract_jtype_imm(u32 insn)
+{
+	return RV_EXTRACT_JTYPE_IMM(insn);
+}
+
+/*
+ * Update a J-type instruction with an immediate value.
+ *
+ * @insn: pointer to the jtype instruction
+ * @imm: the immediate to insert into the instruction
+ */
+static inline void riscv_insn_insert_jtype_imm(u32 *insn, s32 imm)
+{
+	/* drop the old IMMs, all jal IMM bits sit at 31:12 */
+	*insn &= ~GENMASK(31, 12);
+	*insn |= (RV_X(imm, RV_J_IMM_10_1_OFF, RV_J_IMM_10_1_MASK) << RV_J_IMM_10_1_OPOFF) |
+		 (RV_X(imm, RV_J_IMM_11_OFF, RV_J_IMM_11_MASK) << RV_J_IMM_11_OPOFF) |
+		 (RV_X(imm, RV_J_IMM_19_12_OFF, RV_J_IMM_19_12_MASK) << RV_J_IMM_19_12_OPOFF) |
+		 (RV_X(imm, RV_J_IMM_SIGN_OFF, 1) << RV_J_IMM_SIGN_OPOFF);
+}
+
 /*
  * Put together one immediate from a U-type and I-type instruction pair.
  *
diff --git a/arch/riscv/kernel/alternative.c b/arch/riscv/kernel/alternative.c
index 6212ea0eed72..3d4f1f32c7f6 100644
--- a/arch/riscv/kernel/alternative.c
+++ b/arch/riscv/kernel/alternative.c
@@ -79,6 +79,21 @@  static void riscv_alternative_fix_auipc_jalr(void *ptr, u32 auipc_insn,
 	patch_text_nosync(ptr, call, sizeof(u32) * 2);
 }
 
+static void riscv_alternative_fix_jal(void *ptr, u32 jal_insn, int patch_offset)
+{
+	s32 imm;
+
+	/* get and adjust new target address */
+	imm = riscv_insn_extract_jtype_imm(jal_insn);
+	imm -= patch_offset;
+
+	/* update instruction */
+	riscv_insn_insert_jtype_imm(&jal_insn, imm);
+
+	/* patch the call place again */
+	patch_text_nosync(ptr, &jal_insn, sizeof(u32));
+}
+
 void riscv_alternative_fix_offsets(void *alt_ptr, unsigned int len,
 				      int patch_offset)
 {
@@ -106,6 +121,18 @@  void riscv_alternative_fix_offsets(void *alt_ptr, unsigned int len,
 			riscv_alternative_fix_auipc_jalr(alt_ptr + i * sizeof(u32),
 							 insn, insn2, patch_offset);
 		}
+
+		if (riscv_insn_is_jal(insn)) {
+			s32 imm = riscv_insn_extract_jtype_imm(insn);
+
+			/* Don't modify jumps inside the alternative block */
+			if ((alt_ptr + i * sizeof(u32) + imm) >= alt_ptr &&
+			    (alt_ptr + i * sizeof(u32) + imm) < (alt_ptr + len))
+				continue;
+
+			riscv_alternative_fix_jal(alt_ptr + i * sizeof(u32),
+						  insn, patch_offset);
+		}
 	}
 }