linsysfs: expose raw SMBIOS tables

[laffer1]

Summary

• add SMBIOS 3 entry-point discovery and validate SMBIOS 2/3 checksums
• snapshot the entry point and structure table for kernel consumers
• expose /sys/firmware/dmi/tables/smbios_entry_point and /sys/firmware/dmi/tables/DMI through linsysfs as binary mode-0400 files with their actual sizes
• add an ATF regression test for permissions, signatures, checksums, content, and offset reads

Validation

• make -j4 buildkernel KERNCONF=GENERIC
• make -C sys/modules/bios/smbios clean all
• make -C sys/modules/linsysfs clean all
• make -C tests/sys/fs/linsysfs clean all
• sh -n tests/sys/fs/linsysfs/dmi_id_test.sh tests/sys/fs/linsysfs/raw_dmi_test.sh
• C pre-commit cppcheck/clang-format skill (cppcheck clean; formatting churn discarded)
• Splint pre-commit skill (kernel sources skipped as designed)
• tools/build/checkstyle9.pl --patch
• git diff --check
• booted the resulting kernel and verified the raw files return a valid 31-byte _SM_ entry point and 4087-byte DMI table with correct stat sizes and offset reads

Geekbench note

Geekbench 6.4 still prefers /dev/mem when run as root even with these interfaces present. Under Linux emulation it maps physical 0xe0000 for 0x20000 bytes and then faults eight bytes beyond the mapping. The same --sysinfo command succeeds as an unprivileged user. This PR provides the Linux raw SMBIOS ABI, but the root-only Geekbench crash will require separate /dev/mem compatibility handling.

Summary by Sourcery

Expose validated raw SMBIOS tables through linsysfs for Linux-compatible consumers.

New Features:

• Expose raw SMBIOS entry-point and DMI structure table data through Linux-compatible linsysfs paths.

Bug Fixes:

• Validate SMBIOS 2 and SMBIOS 3 entry points and their checksums before use.

Enhancements:

• Snapshot SMBIOS metadata and structure tables for safe kernel consumers and report their actual read-only file sizes.

Build:

• Export the SMBIOS snapshot accessors and add the raw DMI regression test to the test build.

Tests:

• Add ATF coverage for raw SMBIOS file permissions, signatures, checksums, sizes, contents, and offset reads.

[sourcery-ai]

Reviewer's Guide

The PR discovers and validates SMBIOS 2.x/3.x entry points, snapshots the entry point and structure table into kernel-owned buffers, and exposes them as Linux-compatible binary linsysfs files with accurate metadata and offset reads. A root ATF regression test verifies the exported ABI and handles systems without available SMBIOS data.

Sequence diagram for SMBIOS discovery and raw table export

sequenceDiagram
    participant SMBIOS as SMBIOS driver
    participant Firmware as Firmware SMBIOS data
    participant Kernel as Kernel snapshot buffers
    participant Linsysfs as linsysfs
    participant Consumer as Linux consumer

    SMBIOS->>Firmware: smbios_validate_eps()
    Firmware-->>SMBIOS: Valid SMBIOS 2.x or 3.x entry point
    SMBIOS->>Firmware: pmap_mapbios()
    Firmware-->>SMBIOS: Structure table
    SMBIOS->>Kernel: Copy entry point and structure table
    Consumer->>Linsysfs: Read /sys/firmware/dmi/tables/smbios_entry_point
    Linsysfs->>Kernel: smbios_get_entry_point()
    Kernel-->>Linsysfs: Snapshot and actual length
    Linsysfs-->>Consumer: Binary data at requested offset
    Consumer->>Linsysfs: Read /sys/firmware/dmi/tables/DMI
    Linsysfs->>Kernel: smbios_get_structure_table()
    Kernel-->>Linsysfs: Snapshot and actual length
    Linsysfs-->>Consumer: Binary data at requested offset

Loading

File-Level Changes

Change	Details	Files
Add SMBIOS 2.x and 3.x discovery, validation, and bounded table handling.	Prefer the SMBIOS 3 EFI entry point, with SMBIOS 2 fallback. Validate entry-point signatures, lengths, primary and intermediate checksums. Map and snapshot validated entry-point and structure-table data with a maximum table-size bound. Export accessor APIs and module symbols for consumers.	sys/dev/smbios/smbios.c sys/dev/smbios/smbios.h sys/modules/bios/smbios/Makefile
Expose snapshotted SMBIOS data through Linux-compatible linsysfs files.	Create the firmware/dmi/tables hierarchy when both snapshots are available. Provide binary, read-only mode-0400 files with actual sizes. Implement bounded offset and short-read handling for both raw files. Add the SMBIOS module dependency on supported architectures.	sys/compat/linsysfs/linsysfs.c
Add regression coverage for the raw SMBIOS linsysfs ABI.	Register an ATF shell test covering permissions, nonzero sizes, signatures, checksums, full reads, and offset reads. Load and mount linsysfs as needed and skip systems without SMBIOS data. Clean up dynamically loaded modules and mounts.	tests/sys/fs/linsysfs/Makefile tests/sys/fs/linsysfs/raw_dmi_test.sh

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[sourcery-ai]

Hey - I've found 1 issue

Prompt for AI Agents

Please address the comments from this code review:

## Individual Comments

### Comment 1
<location path="sys/dev/smbios/smbios.c" line_range="197-198" />
<code_context>
+		error = ENXIO;
+		goto bad;
+	}
+	eps_data = malloc(eps_len, M_DEVBUF, M_WAITOK);
+	memcpy(eps_data, RES2EPS(sc->res), eps_len);
+
+	if (memcmp(eps_data, SMBIOS3_SIG, 5) == 0) {
</code_context>
<issue_to_address>
**issue (bug_risk):** A legacy SMBIOS 2.1 entry point with length `0x1e` is copied into a 30-byte allocation, but `struct smbios_eps` is 31 bytes and the subsequent `eps->BCD_revision` access reads one byte past that allocation. The preserved 2.1 resource-length workaround is applied only to the bus resource, not to `eps_len` used for the snapshot.

**Triggers:** When firmware provides the SMBIOS 2.1 length workaround entry point with `length == 0x1e`.

**Suggested fix:** Normalize the SMBIOS 2.1 length to `sizeof(struct smbios_eps)` before allocating and copying the snapshot, while preserving the checksum length separately if necessary.

```suggestion
	if (memcmp(RES2EPS(sc->res), SMBIOS_SIG, 4) == 0 &&
	    eps_len == 0x1e)
		eps_len = sizeof(struct smbios_eps);
	eps_data = malloc(eps_len, M_DEVBUF, M_WAITOK);
	memcpy(eps_data, RES2EPS(sc->res), eps_len);
```
</issue_to_address>

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[sourcery-ai]

issue (bug_risk): A legacy SMBIOS 2.1 entry point with length 0x1e is copied into a 30-byte allocation, but struct smbios_eps is 31 bytes and the subsequent eps->BCD_revision access reads one byte past that allocation. The preserved 2.1 resource-length workaround is applied only to the bus resource, not to eps_len used for the snapshot.

Triggers: When firmware provides the SMBIOS 2.1 length workaround entry point with length == 0x1e.

Suggested fix: Normalize the SMBIOS 2.1 length to sizeof(struct smbios_eps) before allocating and copying the snapshot, while preserving the checksum length separately if necessary.

Suggested change

	eps_data = malloc(eps_len, M_DEVBUF, M_WAITOK);
	memcpy(eps_data, RES2EPS(sc->res), eps_len);
	if (memcmp(RES2EPS(sc->res), SMBIOS_SIG, 4) == 0 &&
	eps_len == 0x1e)
	eps_len = sizeof(struct smbios_eps);
	eps_data = malloc(eps_len, M_DEVBUF, M_WAITOK);
	memcpy(eps_data, RES2EPS(sc->res), eps_len);