From: Ahmed Salem x0rw3ll@gmail.com
[ Upstream commit 64b9dfd0776e9c38d733094859a09f13282ce6f8 ]
ACPICA commit 8b83a8d88dfec59ea147fad35fc6deea8859c58c
ap_get_table_length() checks if tables are valid by calling ap_is_valid_header(). The latter then calls ACPI_VALIDATE_RSDP_SIG(Table->Signature).
ap_is_valid_header() accepts struct acpi_table_header as an argument, so the signature size is always fixed to 4 bytes.
The problem is when the string comparison is between ACPI-defined table signature and ACPI_SIG_RSDP. Common ACPI table header specifies the Signature field to be 4 bytes long[1], with the exception of the RSDP structure whose signature is 8 bytes long "RSD PTR " (including the trailing blank character)[2]. Calling strncmp(sig, rsdp_sig, 8) would then result in a sequence overread[3] as sig would be smaller (4 bytes) than the specified bound (8 bytes).
As a workaround, pass the bound conditionally based on the size of the signature being passed.
Link: https://uefi.org/specs/ACPI/6.5_A/05_ACPI_Software_Programming_Model.html#sy... [1] Link: https://uefi.org/specs/ACPI/6.5_A/05_ACPI_Software_Programming_Model.html#ro... [2] Link: https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html#index-Wstringop-over... [3] Link: https://github.com/acpica/acpica/commit/8b83a8d8 Signed-off-by: Ahmed Salem x0rw3ll@gmail.com Signed-off-by: Rafael J. Wysocki rafael.j.wysocki@intel.com Link: https://patch.msgid.link/2248233.Mh6RI2rZIc@rjwysocki.net Signed-off-by: Sasha Levin sashal@kernel.org ---
**YES** This commit should be backported to stable kernel trees. ## Detailed Analysis: ### The Problem The commit fixes a **buffer overread vulnerability** in the `ACPI_VALIDATE_RSDP_SIG` macro. The issue occurs when: 1. **Context**: The macro `ACPI_VALIDATE_RSDP_SIG(a)` calls `strncmp(ACPI_CAST_PTR(char, (a)), ACPI_SIG_RSDP, 8)` 2. **Problem**: When `a` points to a standard ACPI table header (4 bytes signature), but the comparison tries to read 8 bytes for RSDP validation ("RSD PTR "), it reads 4 bytes beyond the allocated signature field 3. **Impact**: This causes a sequence overread that can be detected by tools like GCC's `-Wstringop-overread` and security-focused architectures like CHERI/Morello ### The Fix The fix changes line 530 in `include/acpi/actypes.h`: ```c // Before: #define ACPI_VALIDATE_RSDP_SIG(a) (!strncmp (ACPI_CAST_PTR (char, (a)), ACPI_SIG_RSDP, 8)) // After: #define ACPI_VALIDATE_RSDP_SIG(a) (!strncmp (ACPI_CAST_PTR (char, (a)), ACPI_SIG_RSDP, (sizeof(a) < 8) ? ACPI_NAMESEG_SIZE : 8)) ``` This conditionally limits the comparison to `ACPI_NAMESEG_SIZE` (4 bytes) when the source is smaller than 8 bytes, preventing the overread. ### Why This Should Be Backported: 1. **Security Fix**: This addresses a buffer overread that could be exploited or cause crashes on security-hardened systems 2. **Small & Contained**: The fix is a single line change to a macro definition with minimal risk 3. **Widespread Usage**: The macro is used in multiple critical ACPI code paths: - `drivers/acpi/acpica/tbprint.c` (kernel ACPI table printing) - `tools/power/acpi/tools/acpidump/apdump.c` (ACPI debugging tools) - Various other ACPI validation functions 4. **No Architectural Changes**: This doesn't change functionality, just prevents unsafe memory access 5. **Compiler Warning Fix**: Resolves build warnings with newer GCC versions using `-Wstringop-overread` ### Comparison with Historical Commits: - **Similar to Commit #3 (YES)**: Like the "disable -Wstringop-truncation" commit, this fixes compiler warnings related to string operations, but this one actually fixes the underlying safety issue rather than just suppressing warnings - **Unlike Commits #1,#2,#4,#5 (NO)**: Those were either pure code cleanup, debugging improvements, or infrastructure changes without security implications ### Risk Assessment: - **Minimal Risk**: The fix only affects boundary condition handling in string comparison - **No Functional Impact**: Normal RSDP validation still works correctly for valid 8-byte signatures - **Improves Safety**: Prevents potential memory safety violations on hardened systems This is exactly the type of small, safe, security-focused bugfix that stable trees are designed for.
include/acpi/actypes.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/include/acpi/actypes.h b/include/acpi/actypes.h index 80767e8bf3ad4..d323dfffa4bfc 100644 --- a/include/acpi/actypes.h +++ b/include/acpi/actypes.h @@ -527,7 +527,7 @@ typedef u64 acpi_integer;
/* Support for the special RSDP signature (8 characters) */
-#define ACPI_VALIDATE_RSDP_SIG(a) (!strncmp (ACPI_CAST_PTR (char, (a)), ACPI_SIG_RSDP, 8)) +#define ACPI_VALIDATE_RSDP_SIG(a) (!strncmp (ACPI_CAST_PTR (char, (a)), ACPI_SIG_RSDP, (sizeof(a) < 8) ? ACPI_NAMESEG_SIZE : 8)) #define ACPI_MAKE_RSDP_SIG(dest) (memcpy (ACPI_CAST_PTR (char, (dest)), ACPI_SIG_RSDP, 8))
/* Support for OEMx signature (x can be any character) */