From a676fc8b8e56e7e705966643aa105d2b0818c87e Mon Sep 17 00:00:00 2001 From: Richard Patel Date: Mon, 18 May 2026 18:39:18 +0000 Subject: [PATCH] riscv: cfi: reject unknown flags in PR_SET_CFI prctl(PR_SET_CFI,PR_CFI_BRANCH_LANDING_PADS) silently ignored unknown control values. Only PR_CFI_{ENABLE,DISABLE,LOCK} should be permitted. This is a uABI breaking change (fails previously accepted bits with EINVAL). Fixes: 08ee1559052b ("prctl: cfi: change the branch landing pad prctl()s to be more descriptive") Signed-off-by: Richard Patel Signed-off-by: Linux RISC-V bot --- arch/riscv/include/asm/usercfi.h | 1 + arch/riscv/kernel/usercfi.c | 3 +++ tools/testing/selftests/riscv/cfi/cfitests.c | 6 ++++++ 3 files changed, 10 insertions(+) diff --git a/arch/riscv/include/asm/usercfi.h b/arch/riscv/include/asm/usercfi.h index f56966edbf5c62..61ee02cee29720 100644 --- a/arch/riscv/include/asm/usercfi.h +++ b/arch/riscv/include/asm/usercfi.h @@ -50,6 +50,7 @@ void set_indir_lp_status(struct task_struct *task, bool enable); void set_indir_lp_lock(struct task_struct *task, bool lock); #define PR_SHADOW_STACK_SUPPORTED_STATUS_MASK (PR_SHADOW_STACK_ENABLE) +#define PR_CFI_SUPPORTED_STATUS_MASK (PR_CFI_ENABLE | PR_CFI_DISABLE | PR_CFI_LOCK) #else diff --git a/arch/riscv/kernel/usercfi.c b/arch/riscv/kernel/usercfi.c index cbfb4e495e9f9f..5a7113d69badc2 100644 --- a/arch/riscv/kernel/usercfi.c +++ b/arch/riscv/kernel/usercfi.c @@ -467,6 +467,9 @@ int arch_prctl_set_branch_landing_pad_state(struct task_struct *t, unsigned long if (!is_user_lpad_enabled()) return -EINVAL; + if (state & ~PR_CFI_SUPPORTED_STATUS_MASK) + return -EINVAL; + /* indirect branch tracking is locked and further can't be modified by user */ if (is_indir_lp_locked(t)) return -EINVAL; diff --git a/tools/testing/selftests/riscv/cfi/cfitests.c b/tools/testing/selftests/riscv/cfi/cfitests.c index 39d097b6881ff2..0e3943461e7d83 100644 --- a/tools/testing/selftests/riscv/cfi/cfitests.c +++ b/tools/testing/selftests/riscv/cfi/cfitests.c @@ -141,6 +141,12 @@ int main(int argc, char *argv[]) ksft_print_msg("Starting risc-v tests\n"); + /* Test unknown PR_CFI bits */ + ret = my_syscall5(__NR_prctl, PR_SET_CFI, PR_CFI_BRANCH_LANDING_PADS, + PR_CFI_ENABLE | 0xffff0, 0, 0); + if (!ret) + ksft_exit_fail_msg("PR_SET_CFI accepted reserved branch landing pad bits\n"); + /* * Landing pad test. Not a lot of kernel changes to support landing * pads for user mode except lighting up a bit in senvcfg via a prctl.