On Tue, Aug 30, 2022 at 11:53:13AM -0700, Song Liu wrote:
> From: Miroslav Benes <mbenes@xxxxxxx>
>
> 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 <jpoimboe@xxxxxxxxxx>
> Signed-off-by: Miroslav Benes <mbenes@xxxxxxx>
> Signed-off-by: Song Liu <song@xxxxxxxxxx>
>
> ---
>
> 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@xxxxxxx/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 <SF,EE,ME,IR,DR,RI,LE> 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 <SF,VEC,VSX,EE,PR,FP,ME,IR,DR,RI,LE> 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
