From: Josh Poimboeuf <jpoimboe@kernel.org>
To: Michael Ellerman <mpe@ellerman.id.au>
Cc: live-patching@vger.kernel.org,
Nicholas Piggin <npiggin@gmail.com>,
Christophe Leroy <christophe.leroy@csgroup.eu>,
linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org,
Song Liu <song@kernel.org>
Subject: [PATCH 2/2] powerpc/module_64: Fix "expected nop" error on module re-patching
Date: Tue, 24 Jan 2023 19:38:05 -0800 [thread overview]
Message-ID: <2f6329ffd9674df6ff57e03edeb2ca54414770ab.1674617130.git.jpoimboe@kernel.org> (raw)
In-Reply-To: <cover.1674617130.git.jpoimboe@kernel.org>
When a module with a livepatched function is unloaded and then reloaded,
klp attempts to dynamically re-patch it. On ppc64, that fails with the
following error:
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'
The error happens because the restore r2 instruction had already
previously been written into the klp module's replacement function when
the original function was patched the first time. So the instruction
wasn't a nop as expected.
When the restore r2 instruction has already been patched in, detect that
and skip the warning and the instruction write.
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
---
arch/powerpc/kernel/module_64.c | 14 ++++++++++++--
1 file changed, 12 insertions(+), 2 deletions(-)
diff --git a/arch/powerpc/kernel/module_64.c b/arch/powerpc/kernel/module_64.c
index 016e79bba531..bf1da99fff74 100644
--- a/arch/powerpc/kernel/module_64.c
+++ b/arch/powerpc/kernel/module_64.c
@@ -502,6 +502,7 @@ static unsigned long stub_for_addr(const Elf64_Shdr *sechdrs,
static int restore_r2(const char *name, u32 *instruction, struct module *me)
{
u32 *prev_insn = instruction - 1;
+ u32 insn_val = *instruction;
if (is_mprofile_ftrace_call(name))
return 0;
@@ -514,9 +515,18 @@ static int restore_r2(const char *name, u32 *instruction, struct module *me)
if (!instr_is_relative_link_branch(ppc_inst(*prev_insn)))
return 0;
- if (*instruction != PPC_RAW_NOP()) {
+ /*
+ * For livepatch, the restore r2 instruction might have already been
+ * written previously, if the referenced symbol is in a previously
+ * unloaded module which is now being loaded again. In that case, skip
+ * the warning and the instruction write.
+ */
+ if (insn_val == PPC_INST_LD_TOC)
+ return 0;
+
+ if (insn_val != PPC_RAW_NOP()) {
pr_err("%s: Expected nop after call, got %08x at %pS\n",
- me->name, *instruction, instruction);
+ me->name, insn_val, instruction);
return -ENOEXEC;
}
--
2.39.0
next prev parent reply other threads:[~2023-01-25 3:38 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-01-25 3:38 [PATCH 0/2] powerpc: Fix livepatch module re-patching issue Josh Poimboeuf
2023-01-25 3:38 ` [PATCH 1/2] powerpc/module_64: Improve restore_r2() return semantics Josh Poimboeuf
2023-01-25 5:53 ` Song Liu
2023-01-25 13:24 ` Petr Mladek
2023-01-27 12:38 ` Miroslav Benes
2023-01-25 3:38 ` Josh Poimboeuf [this message]
2023-01-25 6:09 ` [PATCH 2/2] powerpc/module_64: Fix "expected nop" error on module re-patching Song Liu
2023-01-25 16:46 ` Josh Poimboeuf
2023-01-25 17:36 ` Song Liu
2023-01-25 18:53 ` Josh Poimboeuf
2023-01-25 18:58 ` Song Liu
2023-01-25 13:31 ` Petr Mladek
2023-01-27 12:50 ` Miroslav Benes
2023-01-27 13:48 ` [PATCH 0/2] powerpc: Fix livepatch module re-patching issue Joe Lawrence
2023-02-04 17:23 ` Josh Poimboeuf
2023-02-05 0:46 ` Michael Ellerman
2023-02-05 16:21 ` Josh Poimboeuf
2023-02-05 0:46 ` Michael Ellerman
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