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Wed, 31 Aug 2022 19:38:49 +0000 (UTC) Received: from redhat.com (unknown [10.22.32.220]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 3F96D2166B2A; Wed, 31 Aug 2022 19:38:49 +0000 (UTC) Date: Wed, 31 Aug 2022 15:38:47 -0400 From: Joe Lawrence To: Song Liu Subject: Re: [PATCH v5] livepatch: Clear relocation targets on a module removal Message-ID: References: <20220830185313.76402-1-song@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220830185313.76402-1-song@kernel.org> X-Scanned-By: MIMEDefang 2.78 on 10.11.54.6 X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: pmladek@suse.com, x86@kernel.org, jikos@kernel.org, linux-kernel@vger.kernel.org, Josh Poimboeuf , live-patching@vger.kernel.org, mbenes@suse.cz, linuxppc-dev@lists.ozlabs.org, jpoimboe@kernel.org Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On Tue, Aug 30, 2022 at 11:53:13AM -0700, Song Liu wrote: > From: Miroslav Benes > > Josh reported a bug: > > When the object to be patched is a module, and that module is > rmmod'ed and reloaded, it fails to load with: > > module: x86/modules: Skipping invalid relocation target, existing value is nonzero for type 2, loc 00000000ba0302e9, val ffffffffa03e293c > livepatch: failed to initialize patch 'livepatch_nfsd' for module 'nfsd' (-8) > livepatch: patch 'livepatch_nfsd' failed for module 'nfsd', refusing to load module 'nfsd' > > The livepatch module has a relocation which references a symbol > in the _previous_ loading of nfsd. When apply_relocate_add() > tries to replace the old relocation with a new one, it sees that > the previous one is nonzero and it errors out. > > On ppc64le, we have a similar issue: > > module_64: livepatch_nfsd: Expected nop after call, got e8410018 at e_show+0x60/0x548 [livepatch_nfsd] > livepatch: failed to initialize patch 'livepatch_nfsd' for module 'nfsd' (-8) > livepatch: patch 'livepatch_nfsd' failed for module 'nfsd', refusing to load module 'nfsd' > > He also proposed three different solutions. We could remove the error > check in apply_relocate_add() introduced by commit eda9cec4c9a1 > ("x86/module: Detect and skip invalid relocations"). However the check > is useful for detecting corrupted modules. > > We could also deny the patched modules to be removed. If it proved to be > a major drawback for users, we could still implement a different > approach. The solution would also complicate the existing code a lot. > > We thus decided to reverse the relocation patching (clear all relocation > targets on x86_64). The solution is not > universal and is too much arch-specific, but it may prove to be simpler > in the end. > > Reported-by: Josh Poimboeuf > Signed-off-by: Miroslav Benes > Signed-off-by: Song Liu > > --- > > NOTE: powerpc code has not be tested. > > Changes v4 = v5: > 1. Fix compile with powerpc. > > Changes v3 = v4: > 1. Reuse __apply_relocate_add to make it more reliable in long term. > (Josh Poimboeuf) > 2. Add back ppc64 logic from v2, with changes to match current code. > (Josh Poimboeuf) > > Changes v2 => v3: > 1. Rewrite x86 changes to match current code style. > 2. Remove powerpc changes as there is no test coverage in v3. > 3. Only keep 1/3 of v2. > > v2: https://lore.kernel.org/all/20190905124514.8944-1-mbenes@suse.cz/T/#u > --- > arch/powerpc/kernel/module_64.c | 49 +++++++++++++++ > arch/s390/kernel/module.c | 8 +++ > arch/x86/kernel/module.c | 102 +++++++++++++++++++++++--------- > include/linux/moduleloader.h | 7 +++ > kernel/livepatch/core.c | 41 ++++++++++++- > 5 files changed, 179 insertions(+), 28 deletions(-) > > diff --git a/arch/powerpc/kernel/module_64.c b/arch/powerpc/kernel/module_64.c > index 7e45dc98df8a..6aaf5720070d 100644 > --- a/arch/powerpc/kernel/module_64.c > +++ b/arch/powerpc/kernel/module_64.c > @@ -739,6 +739,55 @@ int apply_relocate_add(Elf64_Shdr *sechdrs, > return 0; > } > > +#ifdef CONFIG_LIVEPATCH > +void clear_relocate_add(Elf64_Shdr *sechdrs, > + const char *strtab, > + unsigned int symindex, > + unsigned int relsec, > + struct module *me) > +{ > + unsigned int i; > + Elf64_Rela *rela = (void *)sechdrs[relsec].sh_addr; > + Elf64_Sym *sym; > + unsigned long *location; > + const char *symname; > + u32 *instruction; > + > + pr_debug("Clearing ADD relocate section %u to %u\n", relsec, > + sechdrs[relsec].sh_info); > + > + for (i = 0; i < sechdrs[relsec].sh_size / sizeof(*rela); i++) { > + location = (void *)sechdrs[sechdrs[relsec].sh_info].sh_addr > + + rela[i].r_offset; > + sym = (Elf64_Sym *)sechdrs[symindex].sh_addr > + + ELF64_R_SYM(rela[i].r_info); > + symname = me->core_kallsyms.strtab > + + sym->st_name; > + > + if (ELF64_R_TYPE(rela[i].r_info) != R_PPC_REL24) > + continue; > + /* > + * reverse the operations in apply_relocate_add() for case > + * R_PPC_REL24. > + */ > + if (sym->st_shndx != SHN_UNDEF && > + sym->st_shndx != SHN_LIVEPATCH) > + continue; > + > + instruction = (u32 *)location; > + if (is_mprofile_ftrace_call(symname)) > + continue; > + > + if (!instr_is_relative_link_branch(ppc_inst(*instruction))) > + continue; > + > + instruction += 1; > + *instruction = PPC_RAW_NOP(); > + } > + > +} > +#endif > + > #ifdef CONFIG_DYNAMIC_FTRACE > int module_trampoline_target(struct module *mod, unsigned long addr, > unsigned long *target) > diff --git a/arch/s390/kernel/module.c b/arch/s390/kernel/module.c > index 2d159b32885b..cc6784fbc1ac 100644 > --- a/arch/s390/kernel/module.c > +++ b/arch/s390/kernel/module.c > @@ -500,6 +500,14 @@ static int module_alloc_ftrace_hotpatch_trampolines(struct module *me, > } > #endif /* CONFIG_FUNCTION_TRACER */ > > +#ifdef CONFIG_LIVEPATCH > +void clear_relocate_add(Elf64_Shdr *sechdrs, const char *strtab, > + unsigned int symindex, unsigned int relsec, > + struct module *me) > +{ > +} > +#endif > + > int module_finalize(const Elf_Ehdr *hdr, > const Elf_Shdr *sechdrs, > struct module *me) > diff --git a/arch/x86/kernel/module.c b/arch/x86/kernel/module.c > index b1abf663417c..f9632afbb84c 100644 > --- a/arch/x86/kernel/module.c > +++ b/arch/x86/kernel/module.c > @@ -128,18 +128,20 @@ int apply_relocate(Elf32_Shdr *sechdrs, > return 0; > } > #else /*X86_64*/ > -static int __apply_relocate_add(Elf64_Shdr *sechdrs, > +static int __apply_clear_relocate_add(Elf64_Shdr *sechdrs, > const char *strtab, > unsigned int symindex, > unsigned int relsec, > struct module *me, > - void *(*write)(void *dest, const void *src, size_t len)) > + void *(*write)(void *dest, const void *src, size_t len), > + bool clear) > { > unsigned int i; > Elf64_Rela *rel = (void *)sechdrs[relsec].sh_addr; > Elf64_Sym *sym; > void *loc; > u64 val; > + u64 zero = 0ULL; > > DEBUGP("Applying relocate section %u to %u\n", > relsec, sechdrs[relsec].sh_info); > @@ -163,40 +165,60 @@ static int __apply_relocate_add(Elf64_Shdr *sechdrs, > case R_X86_64_NONE: > break; > case R_X86_64_64: > - if (*(u64 *)loc != 0) > - goto invalid_relocation; > - write(loc, &val, 8); > + if (!clear) { > + if (*(u64 *)loc != 0) > + goto invalid_relocation; > + write(loc, &val, 8); > + } else { > + write(loc, &zero, 8); > + } > break; > case R_X86_64_32: > - if (*(u32 *)loc != 0) > - goto invalid_relocation; > - write(loc, &val, 4); > - if (val != *(u32 *)loc) > - goto overflow; > + if (!clear) { > + if (*(u32 *)loc != 0) > + goto invalid_relocation; > + write(loc, &val, 4); > + if (val != *(u32 *)loc) > + goto overflow; > + } else { > + write(loc, &zero, 4); > + } > break; > case R_X86_64_32S: > - if (*(s32 *)loc != 0) > - goto invalid_relocation; > - write(loc, &val, 4); > - if ((s64)val != *(s32 *)loc) > - goto overflow; > + if (!clear) { > + if (*(s32 *)loc != 0) > + goto invalid_relocation; > + write(loc, &val, 4); > + if ((s64)val != *(s32 *)loc) > + goto overflow; > + } else { > + write(loc, &zero, 4); > + } > break; > case R_X86_64_PC32: > case R_X86_64_PLT32: > - if (*(u32 *)loc != 0) > - goto invalid_relocation; > - val -= (u64)loc; > - write(loc, &val, 4); > + if (!clear) { > + if (*(u32 *)loc != 0) > + goto invalid_relocation; > + val -= (u64)loc; > + write(loc, &val, 4); > #if 0 > - if ((s64)val != *(s32 *)loc) > - goto overflow; > + if ((s64)val != *(s32 *)loc) > + goto overflow; > #endif > + } else { > + write(loc, &zero, 4); > + } > break; > case R_X86_64_PC64: > - if (*(u64 *)loc != 0) > - goto invalid_relocation; > - val -= (u64)loc; > - write(loc, &val, 8); > + if (!clear) { > + if (*(u64 *)loc != 0) > + goto invalid_relocation; > + val -= (u64)loc; > + write(loc, &val, 8); > + } else { > + write(loc, &zero, 8); > + } > break; > default: > pr_err("%s: Unknown rela relocation: %llu\n", > @@ -234,8 +256,8 @@ int apply_relocate_add(Elf64_Shdr *sechdrs, > mutex_lock(&text_mutex); > } > > - ret = __apply_relocate_add(sechdrs, strtab, symindex, relsec, me, > - write); > + ret = __apply_clear_relocate_add(sechdrs, strtab, symindex, relsec, me, > + write, false /* clear */); > > if (!early) { > text_poke_sync(); > @@ -245,6 +267,32 @@ int apply_relocate_add(Elf64_Shdr *sechdrs, > return ret; > } > > +#ifdef CONFIG_LIVEPATCH > + > +void clear_relocate_add(Elf64_Shdr *sechdrs, > + const char *strtab, > + unsigned int symindex, > + unsigned int relsec, > + struct module *me) > +{ > + bool early = me->state == MODULE_STATE_UNFORMED; > + void *(*write)(void *, const void *, size_t) = memcpy; > + > + if (!early) { > + write = text_poke; > + mutex_lock(&text_mutex); > + } > + > + __apply_clear_relocate_add(sechdrs, strtab, symindex, relsec, me, > + write, true /* clear */); > + > + if (!early) { > + text_poke_sync(); > + mutex_unlock(&text_mutex); > + } > +} > +#endif > + > #endif > > int module_finalize(const Elf_Ehdr *hdr, > diff --git a/include/linux/moduleloader.h b/include/linux/moduleloader.h > index 9e09d11ffe5b..d22b36b84b4b 100644 > --- a/include/linux/moduleloader.h > +++ b/include/linux/moduleloader.h > @@ -72,6 +72,13 @@ int apply_relocate_add(Elf_Shdr *sechdrs, > unsigned int symindex, > unsigned int relsec, > struct module *mod); > +#ifdef CONFIG_LIVEPATCH > +void clear_relocate_add(Elf64_Shdr *sechdrs, > + const char *strtab, > + unsigned int symindex, > + unsigned int relsec, > + struct module *me); > +#endif > #else > static inline int apply_relocate_add(Elf_Shdr *sechdrs, > const char *strtab, > diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c > index bc475e62279d..5c0d8a4eba13 100644 > --- a/kernel/livepatch/core.c > +++ b/kernel/livepatch/core.c > @@ -316,6 +316,45 @@ int klp_apply_section_relocs(struct module *pmod, Elf_Shdr *sechdrs, > return apply_relocate_add(sechdrs, strtab, symndx, secndx, pmod); > } > > +static void klp_clear_object_relocations(struct module *pmod, > + struct klp_object *obj) > +{ > + int i, cnt; > + const char *objname, *secname; > + char sec_objname[MODULE_NAME_LEN]; > + Elf_Shdr *sec; > + > + objname = klp_is_module(obj) ? obj->name : "vmlinux"; > + > + /* For each klp relocation section */ > + for (i = 1; i < pmod->klp_info->hdr.e_shnum; i++) { > + sec = pmod->klp_info->sechdrs + i; > + secname = pmod->klp_info->secstrings + sec->sh_name; > + if (!(sec->sh_flags & SHF_RELA_LIVEPATCH)) > + continue; > + > + /* > + * Format: .klp.rela.sec_objname.section_name > + * See comment in klp_resolve_symbols() for an explanation > + * of the selected field width value. > + */ > + secname = pmod->klp_info->secstrings + sec->sh_name; > + cnt = sscanf(secname, ".klp.rela.%55[^.]", sec_objname); > + if (cnt != 1) { > + pr_err("section %s has an incorrectly formatted name\n", > + secname); > + continue; > + } > + > + if (strcmp(objname, sec_objname)) > + continue; > + > + clear_relocate_add(pmod->klp_info->sechdrs, > + pmod->core_kallsyms.strtab, > + pmod->klp_info->symndx, i, pmod); > + } > +} > + > /* > * Sysfs Interface > * > @@ -1154,7 +1193,7 @@ static void klp_cleanup_module_patches_limited(struct module *mod, > klp_unpatch_object(obj); > > klp_post_unpatch_callback(obj); > - > + klp_clear_object_relocations(patch->mod, obj); > klp_free_object_loaded(obj); > break; > } > -- > 2.30.2 > Hi Song, Applying your patch on top of my latest klp-convert-tree branch [1], I modified a few of its late module patching tests (tools/testing/selftests/livepatch/test-song.sh) such that: 1 - A livepatch module is loaded - this module contains klp-relocations to objects in (2) 2 - A target test module is loaded 3 - Unload the test target module - Clear klp-relocations in (1) 4 - Repeat target module load (2) / unload (3) a few times 5 - Unload livepatch module The results: x86_64 : pass s390x : pass ppc64le : crash I suspect Power 32-bit would suffer the same fate, but I don't have hardware to verify. See the kernel log from the crash below... ===== TEST: klp-convert symbols (late module patching) ===== % modprobe test_klp_convert1 test_klp_convert1: tainting kernel with TAINT_LIVEPATCH livepatch: enabling patch 'test_klp_convert1' livepatch: 'test_klp_convert1': starting patching transition livepatch: 'test_klp_convert1': patching complete % modprobe test_klp_convert_mod livepatch: applying patch 'test_klp_convert1' to loading module 'test_klp_convert_mod' test_klp_convert1: saved_command_line, 0: BOOT_IMAGE=(ieee1275//vdevice/v-scsi@30000003/disk@8100000000000000,msdos2)/vmlinuz-5.19.0+ root=/dev/mapper/rhel_ibm--p9z--18--lp7-root ro crashkernel=2G-4G:384M,4G-16G:512M,16G-64G:1G,64G-128G:2G,128G-:4G rd.lvm.lv=rhel_ibm-p9z-18-lp7/root rd.lvm.lv=rhel_ibm-p9z-18-lp7/swap test_klp_convert1: driver_name, 0: test_klp_convert_mod test_klp_convert1: test_klp_get_driver_name(), 0: test_klp_convert_mod test_klp_convert1: homonym_string, 1: homonym string A test_klp_convert1: get_homonym_string(), 1: homonym string A test_klp_convert1: klp_string.12345 = lib/livepatch/test_klp_convert_mod_a.c static string test_klp_convert1: klp_string.67890 = lib/livepatch/test_klp_convert_mod_b.c static string % rmmod test_klp_convert_mod livepatch: reverting patch 'test_klp_convert1' on unloading module 'test_klp_convert_mod' module_64: Clearing ADD relocate section 48 to 6 BUG: Unable to handle kernel data access on write at 0xc008000002140150 Faulting instruction address: 0xc00000000005659c Oops: Kernel access of bad area, sig: 11 [#1] LE PAGE_SIZE=64K MMU=Hash SMP NR_CPUS=2048 NUMA pSeries Modules linked in: test_klp_convert_mod(-) test_klp_convert1(K) bonding tls rfkill pseries_rng drm fuse drm_panel_orientation_quirks xfs libcrc32c sd_mod t10_pi sg ibmvscsi ibmveth scsi_transport_srp vmx_crypto dm_mirror dm_region_hash dm_log dm_mod CPU: 6 PID: 4766 Comm: rmmod Kdump: loaded Tainted: G K 5.19.0+ #1 NIP: c00000000005659c LR: c000000000056590 CTR: 0000000000000024 REGS: c000000007223840 TRAP: 0300 Tainted: G K (5.19.0+) MSR: 8000000000009033 CR: 48008282 XER: 0000000a CFAR: c0000000000a87e0 DAR: c008000002140150 DSISR: 0a000000 IRQMASK: 0 GPR00: c000000000056568 c000000007223ae0 c000000002a68a00 0000000000000001 GPR04: c0080000021706f0 000000000000002d 0000000000000000 0000000000000000 GPR08: 0000000000000066 0000001200000010 0000000000000000 0000000000008000 GPR12: 0000000000000000 c00000000ffca080 0000000000000000 0000000000000000 GPR16: 0000010005bf1810 000000010c0f7370 c0000000011b7e50 c0000000011b7e68 GPR20: c0080000021501c8 c008000002150228 0000000000000030 0000000060000000 GPR24: c008000002160380 c000000056b43000 000000000000ff20 c000000056b43c00 GPR28: aaaaaaaaaaaaaaab c000000056b43b40 0000000000000000 c00800000214014c NIP [c00000000005659c] clear_relocate_add+0x11c/0x1c0 LR [c000000000056590] clear_relocate_add+0x110/0x1c0 Call Trace: [c000000007223ae0] [ffffffffffffffff] 0xffffffffffffffff (unreliable) [c000000007223ba0] [c00000000021e3a8] klp_cleanup_module_patches_limited+0x448/0x480 [c000000007223cb0] [c000000000220278] klp_module_going+0x68/0x94 [c000000007223ce0] [c00000000022f480] __do_sys_delete_module.constprop.0+0x1d0/0x390 [c000000007223db0] [c00000000002f004] system_call_exception+0x164/0x340 [c000000007223e10] [c00000000000be68] system_call_vectored_common+0xe8/0x278 --- interrupt: 3000 at 0x7fffa178fb6c NIP: 00007fffa178fb6c LR: 0000000000000000 CTR: 0000000000000000 REGS: c000000007223e80 TRAP: 3000 Tainted: G K (5.19.0+) MSR: 800000000280f033 CR: 48002482 XER: 00000000 IRQMASK: 0 GPR00: 0000000000000081 00007ffff2d1b720 00007fffa1887200 0000010005bf1878 GPR04: 0000000000000800 000000000000000a 0000000000000000 00000000000000da GPR08: 0000000000000000 0000000000000000 0000000000000000 0000000000000000 GPR12: 0000000000000000 00007fffa201c540 0000000000000000 0000000000000000 GPR16: 0000010005bf1810 000000010c0f7370 000000010c0f8090 000000010c0f8078 GPR20: 000000010c0f8050 000000010c0f80a8 000000010c0f7518 000000010c0f80d0 GPR24: 00007ffff2d1b830 00007ffff2d1efbb 0000000000000000 0000010005bf02a0 GPR28: 00007ffff2d1be50 0000000000000000 0000010005bf1810 0000000000100000 NIP [00007fffa178fb6c] 0x7fffa178fb6c LR [0000000000000000] 0x0 --- interrupt: 3000 Instruction dump: 40820044 813b002c 7ff5f82a 79293664 7d394a14 e9290010 7c69f82e 7fe9fa14 48052235 60000000 2c030000 41820008 <92ff0004> eadb0020 60000000 60000000 ---[ end trace 0000000000000000 ]--- $ addr2line 0xc00000000005659c -e vmlinux /root/klp-convert-tree/arch/powerpc/kernel/module_64.c:785 743 void clear_relocate_add(Elf64_Shdr *sechdrs, 744 const char *strtab, 745 unsigned int symindex, 746 unsigned int relsec, 747 struct module *me) 748 { ... 759 for (i = 0; i < sechdrs[relsec].sh_size / sizeof(*rela); i++) { ... 785 *instruction = PPC_RAW_NOP(); 786 } $ readelf --wide --sections test_klp_convert1.ko | grep -e '\[ 6\]' -e '\[48\]' [ 6] .text.unlikely PROGBITS 0000000000000000 0001b8 0001cc 00 AX 0 0 4 [48] .klp.rela.test_klp_convert_mod..text.unlikely RELA 0000000000000000 041358 000030 18 Ao 45 6 8 $ readelf --wide --relocs test_klp_convert1.ko ... Relocation section '.klp.rela.test_klp_convert_mod..text.unlikely' at offset 0x41358 contains 2 entries: Offset Info Type Symbol's Value Symbol's Name + Addend 00000000000000f0 000000490000000a R_PPC64_REL24 0000000000000000 .klp.sym.test_klp_convert_mod.test_klp_get_driver_name,0 + 0 0000000000000158 000000450000000a R_PPC64_REL24 0000000000000000 .klp.sym.test_klp_convert_mod.get_homonym_string,1 + 0 PS - I will be OOTO for a few weeks in Sept [1] https://github.com/joe-lawrence/klp-convert-tree/tree/klp-convert-v7-devel+song -- Joe