[PATCH v7 04/10] bpf/arm64: mask shift count per RFC 9669

The ARM JIT was not masking the shift count as required by RFC 9669
(0x3f for 64-bit, 0x1f for 32-bit), so large immediate shift counts
overflowed the UBFM/SBFM encoding and failed the JIT. Mask the
immediate in emit_lsl/emit_lsr/emit_asr.

Fixes: 9f4469d9e83a ("bpf/arm: add logical operations")
Cc: [email protected]

Signed-off-by: Stephen Hemminger <[email protected]>
Acked-by: Marat Khalili <[email protected]>
Acked-by: Konstantin Ananyev <[email protected]>
---
 lib/bpf/bpf_jit_arm64.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/lib/bpf/bpf_jit_arm64.c b/lib/bpf/bpf_jit_arm64.c
index ba7ae4d680..7582370062 100644
--- a/lib/bpf/bpf_jit_arm64.c
+++ b/lib/bpf/bpf_jit_arm64.c
@@ -545,12 +545,14 @@ emit_bitfield(struct a64_jit_ctx *ctx, bool is64, uint8_t rd, uint8_t rn,
 	emit_insn(ctx, insn, check_reg(rd) || check_reg(rn) ||
 		  check_immr_imms(is64, immr, imms));
 }
+
 static void
 emit_lsl(struct a64_jit_ctx *ctx, bool is64, uint8_t rd, uint8_t imm)
 {
 	const unsigned int width = is64 ? 64 : 32;
 	uint8_t imms, immr;
 
+	imm &= width - 1;
 	immr = (width - imm) & (width - 1);
 	imms = width - 1 - imm;
 
@@ -560,13 +562,19 @@ emit_lsl(struct a64_jit_ctx *ctx, bool is64, uint8_t rd, uint8_t imm)
 static void
 emit_lsr(struct a64_jit_ctx *ctx, bool is64, uint8_t rd, uint8_t imm)
 {
-	emit_bitfield(ctx, is64, rd, rd, imm, is64 ? 63 : 31, A64_UBFM);
+	const unsigned int width = is64 ? 64 : 32;
+
+	imm &= width - 1;
+	emit_bitfield(ctx, is64, rd, rd, imm, width - 1, A64_UBFM);
 }
 
 static void
 emit_asr(struct a64_jit_ctx *ctx, bool is64, uint8_t rd, uint8_t imm)
 {
-	emit_bitfield(ctx, is64, rd, rd, imm, is64 ? 63 : 31, A64_SBFM);
+	const unsigned int width = is64 ? 64 : 32;
+
+	imm &= width - 1;
+	emit_bitfield(ctx, is64, rd, rd, imm, width - 1, A64_SBFM);
 }
 
 #define A64_AND 0
-- 
2.53.0