From: Josh Poimboeuf jpoimboe@kernel.org
[ Upstream commit 05026ea01e95ffdeb0e5ac8fb7fb1b551e3a8726 ]
If execute_location()'s memcpy of do_nothing() gets inlined and unrolled by the compiler, it copies one word at a time:
mov 0x0(%rip),%rax R_X86_64_PC32 .text+0x1374 mov %rax,0x38(%rbx) mov 0x0(%rip),%rax R_X86_64_PC32 .text+0x136c mov %rax,0x30(%rbx) ...
Those .text references point to the middle of the function, causing objtool to complain about their lack of ENDBR.
Prevent that by resolving the function pointer at runtime rather than build time. This fixes the following warning:
drivers/misc/lkdtm/lkdtm.o: warning: objtool: execute_location+0x23: relocation to !ENDBR: .text+0x1378
Reported-by: kernel test robot lkp@intel.com Signed-off-by: Josh Poimboeuf jpoimboe@kernel.org Signed-off-by: Ingo Molnar mingo@kernel.org Reviewed-by: Kees Cook kees@kernel.org Cc: Arnd Bergmann arnd@arndb.de Cc: Greg Kroah-Hartman gregkh@linuxfoundation.org Cc: Linus Torvalds torvalds@linux-foundation.org Link: https://lore.kernel.org/r/30b9abffbddeb43c4f6320b1270fa9b4d74c54ed.174285284... Closes: https://lore.kernel.org/oe-kbuild-all/202503191453.uFfxQy5R-lkp@intel.com/ Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/misc/lkdtm/perms.c | 14 +++++++++++--- 1 file changed, 11 insertions(+), 3 deletions(-)
diff --git a/drivers/misc/lkdtm/perms.c b/drivers/misc/lkdtm/perms.c index 5b861dbff27e9..6c24426104ba6 100644 --- a/drivers/misc/lkdtm/perms.c +++ b/drivers/misc/lkdtm/perms.c @@ -28,6 +28,13 @@ static const unsigned long rodata = 0xAA55AA55; /* This is marked __ro_after_init, so it should ultimately be .rodata. */ static unsigned long ro_after_init __ro_after_init = 0x55AA5500;
+/* + * This is a pointer to do_nothing() which is initialized at runtime rather + * than build time to avoid objtool IBT validation warnings caused by an + * inlined unrolled memcpy() in execute_location(). + */ +static void __ro_after_init *do_nothing_ptr; + /* * This just returns to the caller. It is designed to be copied into * non-executable memory regions. @@ -65,13 +72,12 @@ static noinline __nocfi void execute_location(void *dst, bool write) { void (*func)(void); func_desc_t fdesc; - void *do_nothing_text = dereference_function_descriptor(do_nothing);
- pr_info("attempting ok execution at %px\n", do_nothing_text); + pr_info("attempting ok execution at %px\n", do_nothing_ptr); do_nothing();
if (write == CODE_WRITE) { - memcpy(dst, do_nothing_text, EXEC_SIZE); + memcpy(dst, do_nothing_ptr, EXEC_SIZE); flush_icache_range((unsigned long)dst, (unsigned long)dst + EXEC_SIZE); } @@ -267,6 +273,8 @@ static void lkdtm_ACCESS_NULL(void)
void __init lkdtm_perms_init(void) { + do_nothing_ptr = dereference_function_descriptor(do_nothing); + /* Make sure we can write to __ro_after_init values during __init */ ro_after_init |= 0xAA; }