[PATCH v8 17/28] x86/insn-eval: Incorporate segment base in linear address computation

[Ricardo Neri]

insn_get_addr_ref() returns the effective address as defined by the
section 3.7.5.1 Vol 1 of the Intel 64 and IA-32 Architectures Software
Developer's Manual. In order to compute the linear address, we must add
to the effective address the segment base address as set in the segment
descriptor. The segment descriptor to use depends on the register used as
operand and segment override prefixes, if any.

In most cases, the segment base address will be 0 if the USER_DS/USER32_DS
segment is used or if segmentation is not used. However, the base address
is not necessarily zero if a user programs defines its own segments. This
is possible by using a local descriptor table.

Since the effective address is a signed quantity, the unsigned segment
base address is saved in a separate variable and added to the final,
unsigned, effective address.

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 | 18 ++++++++++++++++--
 1 file changed, 16 insertions(+), 2 deletions(-)

diff --git a/arch/x86/lib/insn-eval.c b/arch/x86/lib/insn-eval.c
index 04f696c3793e..8ae110a273de 100644
--- a/arch/x86/lib/insn-eval.c
+++ b/arch/x86/lib/insn-eval.c
@@ -673,7 +673,7 @@ int insn_get_modrm_rm_off(struct insn *insn, struct pt_regs *regs)
 void __user *insn_get_addr_ref(struct insn *insn, struct pt_regs *regs)
 {
 	int addr_offset, base_offset, indx_offset;
-	unsigned long linear_addr;
+	unsigned long linear_addr, seg_base_addr;
 	long eff_addr, base, indx;
 	insn_byte_t sib;
 
@@ -687,6 +687,10 @@ void __user *insn_get_addr_ref(struct insn *insn, struct pt_regs *regs)
 			goto out_err;
 
 		eff_addr = regs_get_register(regs, addr_offset);
+
+		seg_base_addr = insn_get_seg_base(regs, insn, addr_offset);
+		if (seg_base_addr == -1L)
+			goto out_err;
 	} else {
 		if (insn->sib.nbytes) {
 			/*
@@ -712,6 +716,11 @@ void __user *insn_get_addr_ref(struct insn *insn, struct pt_regs *regs)
 				indx = regs_get_register(regs, indx_offset);
 
 			eff_addr = base + indx * (1 << X86_SIB_SCALE(sib));
+
+			seg_base_addr = insn_get_seg_base(regs, insn,
+							  base_offset);
+			if (seg_base_addr == -1L)
+				goto out_err;
 		} else {
 			addr_offset = get_reg_offset(insn, regs, REG_TYPE_RM);
 
@@ -730,12 +739,17 @@ void __user *insn_get_addr_ref(struct insn *insn, struct pt_regs *regs)
 			} else {
 				eff_addr = regs_get_register(regs, addr_offset);
 			}
+
+			seg_base_addr = insn_get_seg_base(regs, insn,
+							  addr_offset);
+			if (seg_base_addr == -1L)
+				goto out_err;
 		}
 
 		eff_addr += insn->displacement.value;
 	}
 
-	linear_addr = (unsigned long)eff_addr;
+	linear_addr = (unsigned long)eff_addr + seg_base_addr;
 
 	return (void __user *)linear_addr;
 out_err:
-- 
2.13.0