Bugzilla: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102352
In the Linux kernel, user processes calling into the kernel are essentially threads running in the same address space, of a program that never terminates. This means that using a global variable for the stack protector canary value is problematic on SMP systems, as we can never change it unless we reboot the system. (Processes that sleep for any reason will do so on a call into the kernel, which means that there will always be live kernel stack frames carrying copies of the canary taken when the function was entered) AArch64 implements -mstack-protector-guard=sysreg for this purpose, as this permits the kernel to use different memory addresses for the stack canary for each CPU, and context switch the chosen system register with the rest of the process, allowing each process to use its own unique value for the stack canary. This patch implements something similar, but for the 32-bit ARM kernel, which will start using the user space TLS register TPIDRURO to index per-process metadata while running in the kernel. This means we can just add an offset to TPIDRURO to obtain the address from which to load the canary value. Changes since v4: - add a couple of test cases - incorporate feedback received from Qing and Kyrylo Changes since v3: - force a reload of the TLS register before performing the stack protector check, so that we never rely on the stack for the address of the canary Changes since v2: - fix the template for stack_protect_test_tls so it correctly conveys the fact that it sets the Z flag Cc: Keith Packard <keith...@amazon.com> Cc: thomas.preudho...@celest.fr Cc: adhemerval.zane...@linaro.org Cc: Qing Zhao <qing.z...@oracle.com> Cc: Richard Sandiford <richard.sandif...@arm.com> Cc: Kyrylo Tkachov <kyryo.tkac...@arm.com> Cc: gcc-patches@gcc.gnu.org Ard Biesheuvel (1): [ARM] Add support for TLS register based stack protector canary access gcc/config/arm/arm-opts.h | 6 ++ gcc/config/arm/arm-protos.h | 2 + gcc/config/arm/arm.c | 55 +++++++++++++++ gcc/config/arm/arm.md | 71 +++++++++++++++++++- gcc/config/arm/arm.opt | 22 ++++++ gcc/doc/invoke.texi | 11 +++ gcc/testsuite/gcc.target/arm/stack-protector-7.c | 10 +++ gcc/testsuite/gcc.target/arm/stack-protector-8.c | 5 ++ 8 files changed, 180 insertions(+), 2 deletions(-) create mode 100644 gcc/testsuite/gcc.target/arm/stack-protector-7.c create mode 100644 gcc/testsuite/gcc.target/arm/stack-protector-8.c -- 2.30.2
