[v6 PATCH 12/21] x86/insn: Support both signed 32-bit and 64-bit effective addresses

[Ricardo Neri]

The 32-bit and 64-bit address encodings are identical. This means that we
can use the same function in both cases. In order to reuse the function for
32-bit address encodings, we must sign-extend our 32-bit signed operands to
64-bit signed variables (only for 64-bit builds). To decide on whether sign
extension is needed, we rely on the address size as given by the
instruction structure.

Lastly, before computing the linear address, we must truncate our signed
64-bit signed effective address if the address size is 32-bit.

Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Cc: Adam Buchbinder <adam.buchbinder@xxxxxxxxx>
Cc: Colin Ian King <colin.king@xxxxxxxxxxxxx>
Cc: Lorenzo Stoakes <lstoakes@xxxxxxxxx>
Cc: Qiaowei Ren <qiaowei.ren@xxxxxxxxx>
Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
Cc: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
Cc: Adrian Hunter <adrian.hunter@xxxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: Thomas Garnier <thgarnie@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxx>
Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Cc: Ravi V. Shankar <ravi.v.shankar@xxxxxxxxx>
Cc: x86@xxxxxxxxxx
Signed-off-by: Ricardo Neri <ricardo.neri-calderon@xxxxxxxxxxxxxxx>
---
 arch/x86/lib/insn-eval.c | 44 ++++++++++++++++++++++++++++++++------------
 1 file changed, 32 insertions(+), 12 deletions(-)

diff --git a/arch/x86/lib/insn-eval.c b/arch/x86/lib/insn-eval.c
index edb360f..a9a1704 100644
--- a/arch/x86/lib/insn-eval.c
+++ b/arch/x86/lib/insn-eval.c
@@ -559,6 +559,15 @@ int insn_get_reg_offset_sib_index(struct insn *insn, struct pt_regs *regs)
 	return get_reg_offset(insn, regs, REG_TYPE_INDEX);
 }
 
+static inline long __to_signed_long(unsigned long val, int long_bytes)
+{
+#ifdef CONFIG_X86_64
+	return long_bytes == 4 ? (long)((int)((val) & 0xffffffff)) : (long)val;
+#else
+	return (long)val;
+#endif
+}
+
 /*
  * return the address being referenced be instruction
  * for rm=3 returning the content of the rm reg
@@ -567,19 +576,21 @@ int insn_get_reg_offset_sib_index(struct insn *insn, struct pt_regs *regs)
 void __user *insn_get_addr_ref(struct insn *insn, struct pt_regs *regs)
 {
 	unsigned long linear_addr, seg_base_addr;
-	long eff_addr, base, indx;
-	int addr_offset, base_offset, indx_offset;
+	long eff_addr, base, indx, tmp;
+	int addr_offset, base_offset, indx_offset, addr_bytes;
 	insn_byte_t sib;
 
 	insn_get_modrm(insn);
 	insn_get_sib(insn);
 	sib = insn->sib.value;
+	addr_bytes = insn->addr_bytes;
 
 	if (X86_MODRM_MOD(insn->modrm.value) == 3) {
 		addr_offset = get_reg_offset(insn, regs, REG_TYPE_RM);
 		if (addr_offset < 0)
 			goto out_err;
-		eff_addr = regs_get_register(regs, addr_offset);
+		tmp = regs_get_register(regs, addr_offset);
+		eff_addr = __to_signed_long(tmp, addr_bytes);
 		seg_base_addr = insn_get_seg_base(regs, insn, addr_offset,
 						  false);
 	} else {
@@ -591,20 +602,24 @@ void __user *insn_get_addr_ref(struct insn *insn, struct pt_regs *regs)
 			 * in the address computation.
 			 */
 			base_offset = get_reg_offset(insn, regs, REG_TYPE_BASE);
-			if (unlikely(base_offset == -EDOM))
+			if (unlikely(base_offset == -EDOM)) {
 				base = 0;
-			else if (unlikely(base_offset < 0))
+			} else if (unlikely(base_offset < 0)) {
 				goto out_err;
-			else
-				base = regs_get_register(regs, base_offset);
+			} else {
+				tmp = regs_get_register(regs, base_offset);
+				base = __to_signed_long(tmp, addr_bytes);
+			}
 
 			indx_offset = get_reg_offset(insn, regs, REG_TYPE_INDEX);
-			if (unlikely(indx_offset == -EDOM))
+			if (unlikely(indx_offset == -EDOM)) {
 				indx = 0;
-			else if (unlikely(indx_offset < 0))
+			} else if (unlikely(indx_offset < 0)) {
 				goto out_err;
-			else
-				indx = regs_get_register(regs, indx_offset);
+			} else {
+				tmp = regs_get_register(regs, indx_offset);
+				indx = __to_signed_long(tmp, addr_bytes);
+			}
 
 			eff_addr = base + indx * (1 << X86_SIB_SCALE(sib));
 			seg_base_addr = insn_get_seg_base(regs, insn,
@@ -625,13 +640,18 @@ void __user *insn_get_addr_ref(struct insn *insn, struct pt_regs *regs)
 			} else if (addr_offset < 0) {
 				goto out_err;
 			} else {
-				eff_addr = regs_get_register(regs, addr_offset);
+				tmp = regs_get_register(regs, addr_offset);
+				eff_addr = __to_signed_long(tmp, addr_bytes);
 			}
 			seg_base_addr = insn_get_seg_base(regs, insn,
 							  addr_offset, false);
 		}
 		eff_addr += insn->displacement.value;
 	}
+	/* truncate to 4 bytes for 32-bit effective addresses */
+	if (addr_bytes == 4)
+		eff_addr &= 0xffffffff;
+
 	linear_addr = (unsigned long)eff_addr + seg_base_addr;
 
 	return (void __user *)linear_addr;
-- 
2.9.3