Thank you for your contribution! Sashiko AI review found 3 potential issue(s) to consider: - [High] Incorrect pointer size assumption for 32-bit compat tasks using DW_EH_PE_absptr encoding. - [High] Bypassing speculative execution pointer masking by using an unmasked pointer within a `scoped_user_read_access_size` block. - [Low] Mixing goto-based cleanup labels and scoped_guard declarations in the same function. --
--- Patch [7]: [RFC PATCH v2 07/24] unwind_user/eh_frame: Add support for reading .eh_frame_hdr section --- commit d29ad7450daa52f7e2ed07991186d7ccf95beadb Author: Jens Remus <[email protected]> unwind_user/eh_frame: Add support for reading .eh_frame_hdr section In preparation for unwinding user space stacks with .eh_frame, add basic unwind user eh_frame infrastructure and support for reading the .eh_frame_hdr section. > diff --git a/kernel/unwind/eh_frame.c b/kernel/unwind/eh_frame.c > new file mode 100644 > index 0000000000000..f25a0923e315b > --- /dev/null > +++ b/kernel/unwind/eh_frame.c > @@ -0,0 +1,366 @@ [ ... ] > +static __always_inline int encoded_pointer_size(u8 encoding) > +{ > + u8 format = DW_EH_PE_format(encoding); > + > + switch (format) { > + case DW_EH_PE_absptr: > + return sizeof(unsigned long); [Severity: High] Does hardcoding sizeof(unsigned long) here cause issues for 32-bit compat tasks? If a 64-bit kernel is profiling a 32-bit application, DW_EH_PE_absptr is expected to match the application's native 4-byte pointer size. Using sizeof(unsigned long) means the kernel will read 8 bytes, which could consume too much data and misalign the current pointer for the remainder of the unwinding process. > + case DW_EH_PE_udata2: > + case DW_EH_PE_sdata2: > + return 2; [ ... ] > +static __always_inline int read_encoded_pointer(struct eh_frame_section *sec, > + unsigned long *addr, > + unsigned long end, > + u8 encoding, > + unsigned long *value) > +{ [ ... ] > + /* Read value based on format */ > + switch (format) { > + case DW_EH_PE_absptr: { > + unsigned long tmp; > + UNSAFE_GET_USER_INC(tmp, cur, end, Efault); > + result += tmp; > + break; > + } [Severity: High] Will this also read 8 bytes instead of 4 for a 32-bit task? Similar to encoded_pointer_size(), this reads a full unsigned long for an absolute pointer. If this is a 64-bit kernel unwinding a 32-bit compat application, it seems this might read past the intended data boundaries and corrupt the address parsing. > + case DW_EH_PE_uleb128: { > + unsigned long tmp; [ ... ] > +static int eh_frame_read_header(struct eh_frame_section *sec) > +{ > + struct mm_struct *mm = current->mm; > + void __user *eh_frame_hdr = (void __user *)sec->eh_frame_hdr_start; > + unsigned long cur = sec->eh_frame_hdr_start, end = > sec->eh_frame_hdr_end; [ ... ] > + scoped_user_read_access_size(eh_frame_hdr, end - > sec->eh_frame_hdr_start, > + Efault) { > + /* Read version */ > + UNSAFE_GET_USER_INC(version, cur, end, Efault); [Severity: High] Does this bypass the speculative execution pointer masking provided by scoped_user_read_access_size()? The block masks the eh_frame_hdr pointer, but inside the block, UNSAFE_GET_USER_INC() reads from the unmasked unsigned long cur variable: #define UNSAFE_GET_USER_INC(to, from, end, label) ... unsafe_get_user(__to, (typeof(to) __user *)from, label); Since cur is passed to unsafe_get_user() without being masked, it appears this defeats the Spectre V1 mitigation for architectures relying on can_do_masked_user_access(). > + if (version != 1) > + return -EINVAL; [ ... ] > +int eh_frame_add_section(unsigned long eh_frame_hdr_start, > + unsigned long eh_frame_hdr_end, > + unsigned long text_start, > + unsigned long text_end) > +{ > + struct mm_struct *mm = current->mm; > + struct eh_frame_section *sec; > + int ret; [ ... ] > + scoped_guard(mmap_read_lock, mm) { > + struct vm_area_struct *eh_frame_hdr_vma, *text_vma; > + > + eh_frame_hdr_vma = vma_lookup(mm, eh_frame_hdr_start); [ ... ] > + ret = eh_frame_read_header(sec); > + if (ret) > + goto err_free; > + > + /* TODO nowhere to store it yet - just free it and return an error */ > + ret = -ENOSYS; > + > +err_free: > + free_section(sec); > + return ret; > +} [Severity: Low] This isn't a bug, but should this function avoid mixing scoped_guard() and goto-based error handling? The kernel cleanup guidelines recommend either fully converting to scope-based cleanup (for example, using __free() for the sec allocation) or strictly using goto-based cleanups without scoped_guard(). Mixing them in the same function can create confusing ownership semantics. -- Sashiko AI review ยท https://sashiko.dev/#/patchset/[email protected]?part=7
