Thank you for your contribution! Sashiko AI review found 2 potential issue(s) to consider:
Pre-existing issues: - [High] Missing BTI landing pads (`bti j`) on indirect branch targets in the KPTI trampoline (`__sdei_asm_exit_trampoline` and `tramp_exit`). - [High] The KPTI entry trampoline mapping at `TRAMP_VALIAS` lacks the BTI Guarded Page (`PTE_GP`) attribute, disabling hardware CFI checks. -- --- Patch [1]: [PATCH 01/12] arm64/bti: Add BTI landing pad to __sdei_asm_handler() --- commit 59fadd16326c687a5994c4bec81d9484edcc08f9 Author: Josh Poimboeuf <[email protected]> arm64/bti: Add BTI landing pad to __sdei_asm_handler() With CONFIG_UNMAP_KERNEL_AT_EL0, __sdei_asm_entry_trampoline() indirect jumps to __sdei_asm_handler(). Add "bti j" to prevent a Branch Target exception. > diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S > index e0db14e9c843a..16c21fcb41976 100644 > --- a/arch/arm64/kernel/entry.S > +++ b/arch/arm64/kernel/entry.S > @@ -976,6 +976,7 @@ NOKPROBE(__sdei_asm_exit_trampoline) [Severity: High] This is a pre-existing issue, but do we also need bti j landing pads on the indirect branch targets for the exit paths? For example, __sdei_asm_exit_trampoline() is called via an indirect branch (br x5): arch/arm64/kernel/entry.S:__sdei_asm_exit_trampoline() { SYM_CODE_START(__sdei_asm_exit_trampoline) ldr x4, [x4, #(SDEI_EVENT_INTREGS + S_SDEI_TTBR1)] ... } Similarly, tramp_exit() in the same file lacks a landing pad despite being called via an indirect branch (br x29) on the EL0 exit path: arch/arm64/kernel/entry.S:tramp_exit() { SYM_CODE_START_LOCAL(tramp_exit) tramp_unmap_kernel x29 ... } Would it be better to add bti j annotations to these functions as well to prevent Branch Target exceptions? [Severity: High] This isn't a bug introduced by this patch, but does the KPTI trampoline mapping need the BTI Guarded Page (PTE_GP) attribute? Looking at map_entry_trampoline() in arch/arm64/mm/mmu.c, it uses kernel_exec_prot() to map the trampoline text: arch/arm64/mm/mmu.c:map_entry_trampoline() { pgprot_t prot = kernel_exec_prot(); ... early_create_pgd_mapping(tramp_pg_dir, pa_start, TRAMP_VALIAS, entry_tramp_text_size(), prot, pgd_pgtable_alloc_init_mm, NO_BLOCK_MAPPINGS); } The prot variable is derived from PAGE_KERNEL_ROX, which does not appear to contain the PTE_GP bit. Does this inadvertently disable hardware BTI enforcement for the trampoline pages? If so, could this architectural gap be masking the missing bti j annotations on the trampoline exit paths mentioned above? > * want them. > */ > SYM_CODE_START(__sdei_asm_handler) > + bti j > stp x2, x3, [x1, #SDEI_EVENT_INTREGS + S_PC] > stp x4, x5, [x1, #SDEI_EVENT_INTREGS + 16 * 2] > stp x6, x7, [x1, #SDEI_EVENT_INTREGS + 16 * 3] -- Sashiko AI review ยท https://sashiko.dev/#/patchset/[email protected]?part=1
