On Mon, Mar 10, 2025 at 11:42 PM Deepak Gupta debug@rivosinc.com wrote:
zicfiss / zicfilp introduces a new exception to priv isa `software check exception` with cause code = 18. This patch implements software check exception.
Additionally it implements a cfi violation handler which checks for code in xtval. If xtval=2, it means that sw check exception happened because of an indirect branch not landing on 4 byte aligned PC or not landing on `lpad` instruction or label value embedded in `lpad` not matching label value setup in `x7`. If xtval=3, it means that sw check exception happened because of mismatch between link register (x1 or x5) and top of shadow stack (on execution of `sspopchk`).
In case of cfi violation, SIGSEGV is raised with code=SEGV_CPERR. SEGV_CPERR was introduced by x86 shadow stack patches.
Signed-off-by: Deepak Gupta debug@rivosinc.com
arch/riscv/include/asm/asm-prototypes.h | 1 + arch/riscv/include/asm/entry-common.h | 2 ++ arch/riscv/kernel/entry.S | 3 +++ arch/riscv/kernel/traps.c | 43 +++++++++++++++++++++++++++++++++ 4 files changed, 49 insertions(+)
diff --git a/arch/riscv/include/asm/asm-prototypes.h b/arch/riscv/include/asm/asm-prototypes.h index cd627ec289f1..5a27cefd7805 100644 --- a/arch/riscv/include/asm/asm-prototypes.h +++ b/arch/riscv/include/asm/asm-prototypes.h @@ -51,6 +51,7 @@ DECLARE_DO_ERROR_INFO(do_trap_ecall_u); DECLARE_DO_ERROR_INFO(do_trap_ecall_s); DECLARE_DO_ERROR_INFO(do_trap_ecall_m); DECLARE_DO_ERROR_INFO(do_trap_break); +DECLARE_DO_ERROR_INFO(do_trap_software_check);
asmlinkage void handle_bad_stack(struct pt_regs *regs); asmlinkage void do_page_fault(struct pt_regs *regs); diff --git a/arch/riscv/include/asm/entry-common.h b/arch/riscv/include/asm/entry-common.h index b28ccc6cdeea..34ed149af5d1 100644 --- a/arch/riscv/include/asm/entry-common.h +++ b/arch/riscv/include/asm/entry-common.h @@ -40,4 +40,6 @@ static inline int handle_misaligned_store(struct pt_regs *regs) } #endif
+bool handle_user_cfi_violation(struct pt_regs *regs);
#endif /* _ASM_RISCV_ENTRY_COMMON_H */ diff --git a/arch/riscv/kernel/entry.S b/arch/riscv/kernel/entry.S index 00494b54ff4a..9c00cac3f6f2 100644 --- a/arch/riscv/kernel/entry.S +++ b/arch/riscv/kernel/entry.S @@ -472,6 +472,9 @@ SYM_DATA_START_LOCAL(excp_vect_table) RISCV_PTR do_page_fault /* load page fault */ RISCV_PTR do_trap_unknown RISCV_PTR do_page_fault /* store page fault */
RISCV_PTR do_trap_unknown /* cause=16 */RISCV_PTR do_trap_unknown /* cause=17 */RISCV_PTR do_trap_software_check /* cause=18 is sw check exception */SYM_DATA_END_LABEL(excp_vect_table, SYM_L_LOCAL, excp_vect_table_end)
#ifndef CONFIG_MMU diff --git a/arch/riscv/kernel/traps.c b/arch/riscv/kernel/traps.c index 8ff8e8b36524..3f7709f4595a 100644 --- a/arch/riscv/kernel/traps.c +++ b/arch/riscv/kernel/traps.c @@ -354,6 +354,49 @@ void do_trap_ecall_u(struct pt_regs *regs)
}
+#define CFI_TVAL_FCFI_CODE 2 +#define CFI_TVAL_BCFI_CODE 3 +/* handle cfi violations */ +bool handle_user_cfi_violation(struct pt_regs *regs) +{
bool ret = false;unsigned long tval = csr_read(CSR_TVAL);if ((tval == CFI_TVAL_FCFI_CODE && cpu_supports_indirect_br_lp_instr()) ||(tval == CFI_TVAL_BCFI_CODE && cpu_supports_shadow_stack())) {do_trap_error(regs, SIGSEGV, SEGV_CPERR, regs->epc,"Oops - control flow violation");ret = true;}return ret;+}
+/*
- software check exception is defined with risc-v cfi spec. Software check
- exception is raised when:-
- a) An indirect branch doesn't land on 4 byte aligned PC or `lpad`
- instruction or `label` value programmed in `lpad` instr doesn't
- match with value setup in `x7`. reported code in `xtval` is 2.
- b) `sspopchk` instruction finds a mismatch between top of shadow stack (ssp)
- and x1/x5. reported code in `xtval` is 3.
- */
+asmlinkage __visible __trap_section void do_trap_software_check(struct pt_regs *regs) +{
if (user_mode(regs)) {irqentry_enter_from_user_mode(regs);/* not a cfi violation, then merge into flow of unknown trap handler */if (!handle_user_cfi_violation(regs))do_trap_unknown(regs);irqentry_exit_to_user_mode(regs);} else {/* sw check exception coming from kernel is a bug in kernel */die(regs, "Kernel BUG");}+}
#ifdef CONFIG_MMU asmlinkage __visible noinstr void do_page_fault(struct pt_regs *regs) {
LGTM.
Reviewed-by: Zong Li zong.li@sifive.com
-- 2.34.1
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