gcc-plugins: arm_ssp_per_task_plugin: sign extend the SP mask

The ARM per-task stack protector GCC plugin hits an assert in
the compiler in some case, due to the fact the the SP mask
expression is not sign-extended as it should be. So fix that.

Suggested-by: Kugan Vivekanandarajah <kugan.vivekanandarajah@linaro.org>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Kees Cook <keescook@chromium.org>

1 files changed, 3 insertions, 2 deletions

diff --git a/scripts/gcc-plugins/arm_ssp_per_task_plugin.c b/scripts/gcc-plugins/arm_ssp_per_task_plugin.c
index de70b8470971..a65fbefb8501 100644
--- a/scripts/gcc-plugins/arm_ssp_per_task_plugin.c
+++ b/scripts/gcc-plugins/arm_ssp_per_task_plugin.c
@@ -13,7 +13,7 @@ static unsigned int arm_pertask_ssp_rtl_execute(void)
         for (insn = get_insns(); insn; insn = NEXT_INSN(insn)) {
                 const char *sym;
                 rtx body;
-                rtx masked_sp;
+                rtx mask, masked_sp;
 
                 /*
                  * Find a SET insn involving a SYMBOL_REF to __stack_chk_guard
@@ -33,12 +33,13 @@ static unsigned int arm_pertask_ssp_rtl_execute(void)
                  * produces the address of the copy of the stack canary value
                  * stored in struct thread_info
                  */
+                mask = GEN_INT(sext_hwi(sp_mask, GET_MODE_PRECISION(Pmode)));
                 masked_sp = gen_reg_rtx(Pmode);
 
                 emit_insn_before(gen_rtx_SET(masked_sp,
                                              gen_rtx_AND(Pmode,
                                                          stack_pointer_rtx,
-                                                         GEN_INT(sp_mask))),
+                                                         mask)),
                                  insn);
 
                 SET_SRC(body) = gen_rtx_PLUS(Pmode, masked_sp,