arm: Clear canary value after stack_protect_test [PR96191]

The stack_protect_test patterns were leaving the canary value in the
temporary register, meaning that it was often still in registers on
return from the function.  An attacker might therefore have been
able to use it to defeat stack-smash protection for a later function.

gcc/
	PR target/96191
	* config/arm/arm.md (arm_stack_protect_test_insn): Zero out
	operand 2 after use.
	* config/arm/thumb1.md (thumb1_stack_protect_test_insn): Likewise.

gcc/testsuite/
	* gcc.target/arm/stack-protector-1.c: New test.
	* gcc.target/arm/stack-protector-2.c: Likewise.

diff --git a/gcc/config/arm/arm.md b/gcc/config/arm/arm.md
index a6a31f8..dd13c77 100644 (file)
--- a/gcc/config/arm/arm.md
+++ b/gcc/config/arm/arm.md
@@ -9320,6 +9320,8 @@
   [(set_attr "arch" "t1,32")]
 )
 
+;; DO NOT SPLIT THIS PATTERN.  It is important for security reasons that the
+;; canary value does not live beyond the end of this sequence.
 (define_insn "arm_stack_protect_test_insn"
   [(set (reg:CC_Z CC_REGNUM)
        (compare:CC_Z (unspec:SI [(match_operand:SI 1 "memory_operand" "m,m")
@@ -9329,8 +9331,8 @@
    (clobber (match_operand:SI 0 "register_operand" "=&l,&r"))
    (clobber (match_dup 2))]
   "TARGET_32BIT"
-  "ldr\t%0, [%2]\;ldr\t%2, %1\;eors\t%0, %2, %0"
-  [(set_attr "length" "8,12")
+  "ldr\t%0, [%2]\;ldr\t%2, %1\;eors\t%0, %2, %0\;mov\t%2, #0"
+  [(set_attr "length" "12,16")
    (set_attr "conds" "set")
    (set_attr "type" "multiple")
    (set_attr "arch" "t,32")]

diff --git a/gcc/config/arm/thumb1.md b/gcc/config/arm/thumb1.md
index 2486163..0ff8190 100644 (file)
--- a/gcc/config/arm/thumb1.md
+++ b/gcc/config/arm/thumb1.md
@@ -2020,6 +2020,8 @@
   [(set_attr "type" "mov_reg")]
 )
 
+;; DO NOT SPLIT THIS PATTERN.  It is important for security reasons that the
+;; canary value does not live beyond the end of this sequence.
 (define_insn "thumb1_stack_protect_test_insn"
   [(set (match_operand:SI 0 "register_operand" "=&l")
        (unspec:SI [(match_operand:SI 1 "memory_operand" "m")
@@ -2027,9 +2029,9 @@
         UNSPEC_SP_TEST))
    (clobber (match_dup 2))]
   "TARGET_THUMB1"
-  "ldr\t%0, [%2]\;ldr\t%2, %1\;eors\t%0, %2, %0"
-  [(set_attr "length" "8")
-   (set_attr "conds" "set")
+  "ldr\t%0, [%2]\;ldr\t%2, %1\;eors\t%0, %2, %0\;movs\t%2, #0"
+  [(set_attr "length" "10")
+   (set_attr "conds" "clob")
    (set_attr "type" "multiple")]
 )
 \f

diff --git a/gcc/testsuite/gcc.target/arm/stack-protector-1.c b/gcc/testsuite/gcc.target/arm/stack-protector-1.c
new file mode 100644 (file)
index 0000000..b03ea14
--- /dev/null
+++ b/gcc/testsuite/gcc.target/arm/stack-protector-1.c
@@ -0,0 +1,63 @@
+/* { dg-do run } */
+/* { dg-require-effective-target fstack_protector } */
+/* { dg-options "-fstack-protector-all -O2" } */
+
+extern volatile long *stack_chk_guard_ptr;
+
+volatile long *
+get_ptr (void)
+{
+  return stack_chk_guard_ptr;
+}
+
+void __attribute__ ((noipa))
+f (void)
+{
+  volatile int x;
+  x = 1;
+  x += 1;
+}
+
+#define CHECK(REG) "\tcmp\tr0, " #REG "\n\tbeq\t1f\n"
+
+asm (
+"      .data\n"
+"      .align  3\n"
+"      .globl  stack_chk_guard_ptr\n"
+"stack_chk_guard_ptr:\n"
+"      .word   __stack_chk_guard\n"
+"      .weak   __stack_chk_guard\n"
+"__stack_chk_guard:\n"
+"      .word   0xdead4321\n"
+"      .text\n"
+"      .globl  main\n"
+"      .type   main, %function\n"
+"main:\n"
+"      bl      get_ptr\n"
+"      str     r0, [sp, #-8]!\n"
+"      bl      f\n"
+"      str     r0, [sp, #4]\n"
+"      ldr     r0, [sp]\n"
+"      ldr     r0, [r0]\n"
+       CHECK (r1)
+       CHECK (r2)
+       CHECK (r3)
+       CHECK (r4)
+       CHECK (r5)
+       CHECK (r6)
+       CHECK (r7)
+       CHECK (r8)
+       CHECK (r9)
+       CHECK (r10)
+       CHECK (r11)
+       CHECK (r12)
+       CHECK (r13)
+       CHECK (r14)
+"      ldr     r1, [sp, #4]\n"
+       CHECK (r1)
+"      mov     r0, #0\n"
+"      b       exit\n"
+"1:\n"
+"      b       abort\n"
+"      .size   main, .-main"
+);

diff --git a/gcc/testsuite/gcc.target/arm/stack-protector-2.c b/gcc/testsuite/gcc.target/arm/stack-protector-2.c
new file mode 100644 (file)
index 0000000..266c36f
--- /dev/null
+++ b/gcc/testsuite/gcc.target/arm/stack-protector-2.c
@@ -0,0 +1,6 @@
+/* { dg-do run } */
+/* { dg-require-effective-target fstack_protector } */
+/* { dg-require-effective-target fpic } */
+/* { dg-options "-fstack-protector-all -O2 -fpic" } */
+
+#include "stack-protector-1.c"