Re: [PATCH v8 05/28] x86/mpx: Use signed variables to compute effective addresses

[Borislav Petkov]

On Fri, Aug 18, 2017 at 05:27:46PM -0700, Ricardo Neri wrote:
> Even though memory addresses are unsigned, the operands used to compute the
> effective address do have a sign. This is true for ModRM.rm, SIB.base,
> SIB.index as well as the displacement bytes. Thus, signed variables shall
> be used when computing the effective address from these operands. Once the
> signed effective address has been computed, it is casted to an unsigned
> long to determine the linear address.
> 
> Variables are renamed to better reflect the type of address being
> computed.
> 
> Cc: Borislav Petkov <bp@xxxxxxx>
> Cc: Andy Lutomirski <luto@xxxxxxxxxx>
> 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: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Cc: Nathan Howard <liverlint@xxxxxxxxx>
> Cc: Adan Hawthorn <adanhawthorn@xxxxxxxxx>
> Cc: Joe Perches <joe@xxxxxxxxxxx>
> Cc: Ravi V. Shankar <ravi.v.shankar@xxxxxxxxx>
> Cc: x86@xxxxxxxxxx
> Signed-off-by: Ricardo Neri <ricardo.neri-calderon@xxxxxxxxxxxxxxx>
> ---
>  arch/x86/mm/mpx.c | 20 ++++++++++++++------
>  1 file changed, 14 insertions(+), 6 deletions(-)

I think you can simplify this function even more (diff ontop):

diff --git a/arch/x86/mm/mpx.c b/arch/x86/mm/mpx.c
index 9eec98022510..d0ec5c9b2a57 100644
--- a/arch/x86/mm/mpx.c
+++ b/arch/x86/mm/mpx.c
@@ -139,7 +139,7 @@ static int get_reg_offset(struct insn *insn, struct pt_regs *regs,
 static void __user *mpx_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 = -1;
 	long eff_addr, base, indx;
 	insn_byte_t sib;
 
@@ -150,18 +150,18 @@ static void __user *mpx_get_addr_ref(struct insn *insn, struct pt_regs *regs)
 	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;
+			goto out;
 
 		eff_addr = regs_get_register(regs, addr_offset);
 	} else {
 		if (insn->sib.nbytes) {
 			base_offset = get_reg_offset(insn, regs, REG_TYPE_BASE);
 			if (base_offset < 0)
-				goto out_err;
+				goto out;
 
 			indx_offset = get_reg_offset(insn, regs, REG_TYPE_INDEX);
 			if (indx_offset < 0)
-				goto out_err;
+				goto out;
 
 			base = regs_get_register(regs, base_offset);
 			indx = regs_get_register(regs, indx_offset);
@@ -170,7 +170,7 @@ static void __user *mpx_get_addr_ref(struct insn *insn, struct pt_regs *regs)
 		} else {
 			addr_offset = get_reg_offset(insn, regs, REG_TYPE_RM);
 			if (addr_offset < 0)
-				goto out_err;
+				goto out;
 
 			eff_addr = regs_get_register(regs, addr_offset);
 		}
@@ -180,9 +180,8 @@ static void __user *mpx_get_addr_ref(struct insn *insn, struct pt_regs *regs)
 
 	linear_addr = (unsigned long)eff_addr;
 
+out:
 	return (void __user *)linear_addr;
-out_err:
-	return (void __user *)-1;
 }
 
 static int mpx_insn_decode(struct insn *insn,

-- 
Regards/Gruss,
    Boris.

SUSE Linux GmbH, GF: Felix ImendÃrffer, Jane Smithard, Graham Norton, HRB 21284 (AG NÃrnberg)
--