arm/arm64: smccc-1.1: Handle function result as parameters

Marc Zyngier · wildea01 · commit 755a8bf5579d · 2018-08-30T14:18:03.000+01:00
If someone has the silly idea to write something along those lines: extern u64 foo(void); void bar(struct arm_smccc_res *res) { arm_smccc_1_1_smc(0xbad, foo(), res); } they are in for a surprise, as this gets compiled as: 0000000000000588 <bar>: 588: a9be7bfd stp x29, x30, [sp, #-32]! 58c: 910003fd mov x29, sp 590: f9000bf3 str x19, [sp, torvalds#16] 594: aa0003f3 mov x19, x0 598: aa1e03e0 mov x0, x30 59c: 94000000 bl 0 <_mcount> 5a0: 94000000 bl 0 <foo> 5a4: aa0003e1 mov x1, x0 5a8: d4000003 smc #0x0 5ac: b4000073 cbz x19, 5b8 <bar+0x30> 5b0: a9000660 stp x0, x1, [x19] 5b4: a9010e62 stp x2, x3, [x19, torvalds#16] 5b8: f9400bf3 ldr x19, [sp, torvalds#16] 5bc: a8c27bfd ldp x29, x30, [sp], torvalds#32 5c0: d65f03c0 ret 5c4: d503201f nop The call to foo "overwrites" the x0 register for the return value, and we end up calling the wrong secure service. A solution is to evaluate all the parameters before assigning anything to specific registers, leading to the expected result: 0000000000000588 <bar>: 588: a9be7bfd stp x29, x30, [sp, #-32]! 58c: 910003fd mov x29, sp 590: f9000bf3 str x19, [sp, torvalds#16] 594: aa0003f3 mov x19, x0 598: aa1e03e0 mov x0, x30 59c: 94000000 bl 0 <_mcount> 5a0: 94000000 bl 0 <foo> 5a4: aa0003e1 mov x1, x0 5a8: d28175a0 mov x0, #0xbad 5ac: d4000003 smc #0x0 5b0: b4000073 cbz x19, 5bc <bar+0x34> 5b4: a9000660 stp x0, x1, [x19] 5b8: a9010e62 stp x2, x3, [x19, torvalds#16] 5bc: f9400bf3 ldr x19, [sp, torvalds#16] 5c0: a8c27bfd ldp x29, x30, [sp], torvalds#32 5c4: d65f03c0 ret Reported-by: Julien Grall <julien.grall@arm.com> Signed-off-by: Marc Zyngier <marc.zyngier@arm.com> Signed-off-by: Will Deacon <will.deacon@arm.com>
diff --git a/include/linux/arm-smccc.h b/include/linux/arm-smccc.h
@@ -205,41 +205,51 @@ asmlinkage void __arm_smccc_hvc(unsigned long a0, unsigned long a1,
 	register unsigned long r3 asm("r3")
 
 #define __declare_arg_1(a0, a1, res)					\
+	typeof(a1) __a1 = a1;						\
 	struct arm_smccc_res   *___res = res;				\
 	register unsigned long r0 asm("r0") = (u32)a0;			\
-	register unsigned long r1 asm("r1") = a1;			\
+	register unsigned long r1 asm("r1") = __a1;			\
 	register unsigned long r2 asm("r2");				\
 	register unsigned long r3 asm("r3")
 
 #define __declare_arg_2(a0, a1, a2, res)				\
+	typeof(a1) __a1 = a1;						\
+	typeof(a2) __a2 = a2;						\
 	struct arm_smccc_res   *___res = res;				\
 	register unsigned long r0 asm("r0") = (u32)a0;			\
-	register unsigned long r1 asm("r1") = a1;			\
-	register unsigned long r2 asm("r2") = a2;			\
+	register unsigned long r1 asm("r1") = __a1;			\
+	register unsigned long r2 asm("r2") = __a2;			\
 	register unsigned long r3 asm("r3")
 
 #define __declare_arg_3(a0, a1, a2, a3, res)				\
+	typeof(a1) __a1 = a1;						\
+	typeof(a2) __a2 = a2;						\
+	typeof(a3) __a3 = a3;						\
 	struct arm_smccc_res   *___res = res;				\
 	register unsigned long r0 asm("r0") = (u32)a0;			\
-	register unsigned long r1 asm("r1") = a1;			\
-	register unsigned long r2 asm("r2") = a2;			\
-	register unsigned long r3 asm("r3") = a3
+	register unsigned long r1 asm("r1") = __a1;			\
+	register unsigned long r2 asm("r2") = __a2;			\
+	register unsigned long r3 asm("r3") = __a3
 
 #define __declare_arg_4(a0, a1, a2, a3, a4, res)			\
+	typeof(a4) __a4 = a4;						\
 	__declare_arg_3(a0, a1, a2, a3, res);				\
-	register typeof(a4) r4 asm("r4") = a4
+	register unsigned long r4 asm("r4") = __a4
 
 #define __declare_arg_5(a0, a1, a2, a3, a4, a5, res)			\
+	typeof(a5) __a5 = a5;						\
 	__declare_arg_4(a0, a1, a2, a3, a4, res);			\
-	register typeof(a5) r5 asm("r5") = a5
+	register unsigned long r5 asm("r5") = __a5
 
 #define __declare_arg_6(a0, a1, a2, a3, a4, a5, a6, res)		\
+	typeof(a6) __a6 = a6;						\
 	__declare_arg_5(a0, a1, a2, a3, a4, a5, res);			\
-	register typeof(a6) r6 asm("r6") = a6
+	register unsigned long r6 asm("r6") = __a6
 
 #define __declare_arg_7(a0, a1, a2, a3, a4, a5, a6, a7, res)		\
+	typeof(a7) __a7 = a7;						\
 	__declare_arg_6(a0, a1, a2, a3, a4, a5, a6, res);		\
-	register typeof(a7) r7 asm("r7") = a7
+	register unsigned long r7 asm("r7") = __a7
 
 #define ___declare_args(count, ...) __declare_arg_ ## count(__VA_ARGS__)
 #define __declare_args(count, ...)  ___declare_args(count, __VA_ARGS__)
