[PATCH v4 10/17] insn/eval: Incorporate segment base in 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 truly give the linear address, we must
add the effective address to the segment base as described by the segment
descriptor.

In most cases, the base will be 0 if the USER_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.

Cc: Dave Hansen 
Cc: Adam Buchbinder 
Cc: Colin Ian King 
Cc: Lorenzo Stoakes 
Cc: Qiaowei Ren 
Cc: Arnaldo Carvalho de Melo 
Cc: Masami Hiramatsu 
Cc: Adrian Hunter 
Cc: Kees Cook 
Cc: Thomas Garnier 
Cc: Peter Zijlstra 
Cc: Borislav Petkov 
Cc: Dmitry Vyukov 
Cc: Ravi V. Shankar 
Cc: [e-mail]
Signed-off-by: Ricardo Neri 
---
 arch/x86/lib/insn-eval.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/arch/x86/lib/insn-eval.c b/arch/x86/lib/insn-eval.c
index d6525c2..b3a2fe8 100644
--- a/arch/x86/lib/insn-eval.c
+++ b/arch/x86/lib/insn-eval.c
@@ -523,6 +523,7 @@ static void __user *insn_get_addr_ref(struct insn *insn, struct pt_regs *regs)
    	if (addr_offset < 0)
    		goto out_err;
    	addr = regs_get_register(regs, addr_offset);
+		addr += insn_get_seg_base(regs, insn, addr_offset);
    } else {
    	if (insn->sib.nbytes) {
    		/*
@@ -551,6 +552,7 @@ static void __user *insn_get_addr_ref(struct insn *insn, struct pt_regs *regs)
    			indx = regs_get_register(regs, indx_offset);

addr = base + indx * (1 << X86_SIB_SCALE(sib));
+			addr += insn_get_seg_base(regs, insn, base_offset);
    	} else {
    		unsigned char addr_bytes;

@@ -575,8 +577,10 @@ static void __user *insn_get_addr_ref(struct insn *insn, struct pt_regs *regs)
    		} else {
    			addr = regs_get_register(regs, addr_offset);
    		}
+			addr += insn_get_seg_base(regs, insn, addr_offset);
    	}
    	addr += insn->displacement.value;
+
    }
    return (void __user *)addr;
 out_err: