On Wed, Feb 10, 2021 at 04:36:08PM -0800, Stephen Boyd wrote: > Quoting Greg Kroah-Hartman (2020-12-09 06:51:33) > > On Tue, Dec 08, 2020 at 01:20:56PM -0800, Kees Cook wrote: > > > On Mon, Dec 07, 2020 at 05:05:33PM +0000, Mark Rutland wrote: > > > > When building with KASAN and LKDTM, clang may implictly generate an > > > > asan.module_ctor function in the LKDTM rodata object. The Makefile moves > > > > the lkdtm_rodata_do_nothing() function into .rodata by renaming the > > > > file's .text section to .rodata, and consequently also moves the ctor > > > > function into .rodata, leading to a boot time crash (splat below) when > > > > the ctor is invoked by do_ctors(). > > > > > > > > Let's prevent this by marking the function as noinstr rather than > > > > notrace, and renaming the file's .noinstr.text to .rodata. Marking the > > > > function as noinstr will prevent tracing and kprobes, and will inhibit > > > > any undesireable compiler instrumentation. > > > > > > > > The ctor function (if any) will be placed in .text and will work > > > > correctly. > > > > > > > > Example splat before this patch is applied: > > > > > > > > [ 0.916359] Unable to handle kernel execute from non-executable memory at virtual address ffffa0006b60f5ac > > > > [ 0.922088] Mem abort info: > > > > [ 0.922828] ESR = 0x8600000e > > > > [ 0.923635] EC = 0x21: IABT (current EL), IL = 32 bits > > > > [ 0.925036] SET = 0, FnV = 0 > > > > [ 0.925838] EA = 0, S1PTW = 0 > > > > [ 0.926714] swapper pgtable: 4k pages, 48-bit VAs, pgdp=00000000427b3000 > > > > [ 0.928489] [ffffa0006b60f5ac] pgd=000000023ffff003, p4d=000000023ffff003, pud=000000023fffe003, pmd=0068000042000f01 > > > > [ 0.931330] Internal error: Oops: 8600000e [#1] PREEMPT SMP > > > > [ 0.932806] Modules linked in: > > > > [ 0.933617] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.10.0-rc7 #2 > > > > [ 0.935620] Hardware name: linux,dummy-virt (DT) > > > > [ 0.936924] pstate: 40400005 (nZcv daif +PAN -UAO -TCO BTYPE=--) > > > > [ 0.938609] pc : asan.module_ctor+0x0/0x14 > > > > [ 0.939759] lr : do_basic_setup+0x4c/0x70 > > > > [ 0.940889] sp : ffff27b600177e30 > > > > [ 0.941815] x29: ffff27b600177e30 x28: 0000000000000000 > > > > [ 0.943306] x27: 0000000000000000 x26: 0000000000000000 > > > > [ 0.944803] x25: 0000000000000000 x24: 0000000000000000 > > > > [ 0.946289] x23: 0000000000000001 x22: 0000000000000000 > > > > [ 0.947777] x21: ffffa0006bf4a890 x20: ffffa0006befb6c0 > > > > [ 0.949271] x19: ffffa0006bef9358 x18: 0000000000000068 > > > > [ 0.950756] x17: fffffffffffffff8 x16: 0000000000000000 > > > > [ 0.952246] x15: 0000000000000000 x14: 0000000000000000 > > > > [ 0.953734] x13: 00000000838a16d5 x12: 0000000000000001 > > > > [ 0.955223] x11: ffff94000da74041 x10: dfffa00000000000 > > > > [ 0.956715] x9 : 0000000000000000 x8 : ffffa0006b60f5ac > > > > [ 0.958199] x7 : f9f9f9f9f9f9f9f9 x6 : 000000000000003f > > > > [ 0.959683] x5 : 0000000000000040 x4 : 0000000000000000 > > > > [ 0.961178] x3 : ffffa0006bdc15a0 x2 : 0000000000000005 > > > > [ 0.962662] x1 : 00000000000000f9 x0 : ffffa0006bef9350 > > > > [ 0.964155] Call trace: > > > > [ 0.964844] asan.module_ctor+0x0/0x14 > > > > [ 0.965895] kernel_init_freeable+0x158/0x198 > > > > [ 0.967115] kernel_init+0x14/0x19c > > > > [ 0.968104] ret_from_fork+0x10/0x30 > > > > [ 0.969110] Code: 00000003 00000000 00000000 00000000 (00000000) > > > > [ 0.970815] ---[ end trace b5339784e20d015c ]--- > > > > > > > > Signed-off-by: Mark Rutland <mark.rutland@xxxxxxx> > > > > > > Oh, eek. Why was a ctor generated at all? But yes, this looks good. > > > Greg, can you pick this up please? > > > > > > Acked-by: Kees Cook <keescook@xxxxxxxxxxxx> > > > > Now picked up, thanks. > > > > Can this be backported to 5.4 and 5.10 stable trees? I just ran across > this trying to use kasan on 5.4 with lkdtm and it blows up early. This > patch applies on 5.4 cleanly but doesn't compile because it's missing > noinstr. Here's a version of the patch that introduces noinstr on 5.4.97 > so this patch can be picked to 5.4 stable trees. Why 5.10? This showed up in 5.8, so how would it be needed there? confused, greg k-h
