From: Sven Schnelle <svens@linux.ibm.com> To: Mark Rutland <mark.rutland@arm.com> Cc: Steven Rostedt <rostedt@goodmis.org>, Yinan Liu <yinan@linux.alibaba.com>, linuxppc-dev@lists.ozlabs.org, Sachin Sant <sachinp@linux.ibm.com>, linux-kernel@vger.kernel.org, ardb@kernel.org, keescook@chromium.org, hca@linux.ibm.com Subject: Re: [powerpc] ftrace warning kernel/trace/ftrace.c:2068 with code-patching selftests Date: Thu, 27 Jan 2022 14:16:31 +0100 [thread overview] Message-ID: <yt9dsft9gvyo.fsf@linux.ibm.com> (raw) In-Reply-To: <YfKZXvB9vCN1bA1c@FVFF77S0Q05N> (Mark Rutland's message of "Thu, 27 Jan 2022 13:08:46 +0000") Mark Rutland <mark.rutland@arm.com> writes: > On Thu, Jan 27, 2022 at 07:46:01AM -0500, Steven Rostedt wrote: >> On Thu, 27 Jan 2022 12:27:04 +0000 >> Mark Rutland <mark.rutland@arm.com> wrote: >> >> > Ah, so those non-ELF relocations for the mcount_loc table just mean "apply the >> > KASLR offset here", which is equivalent for all entries. >> > >> > That makes sense, thanks! >> >> And this is why we were having such a hard time understanding each other ;-) > > ;) > > With that in mind, I think that we understand that the build-time sort works > for: > > * arch/x86, becuase the non-ELF relocations for mcount_loc happen to be > equivalent. > > * arch/arm, because there's no dynamic relocaiton and the mcount_loc entries > have been finalized prior to sorting. > > ... but doesn't work for anyone else (including arm64) because the ELF > relocations are not equivalent, and need special care that is not yet > implemented. For s390 my idea is to just skip the addresses between __start_mcount_loc and __stop_mcount_loc, because for these addresses we know that they are 64 bits wide, so we just need to add the KASLR offset. I'm thinking about something like this: diff --git a/arch/s390/boot/compressed/decompressor.h b/arch/s390/boot/compressed/decompressor.h index f75cc31a77dd..015d7e2e94ef 100644 --- a/arch/s390/boot/compressed/decompressor.h +++ b/arch/s390/boot/compressed/decompressor.h @@ -25,6 +25,8 @@ struct vmlinux_info { unsigned long rela_dyn_start; unsigned long rela_dyn_end; unsigned long amode31_size; + unsigned long start_mcount_loc; + unsigned long stop_mcount_loc; }; /* Symbols defined by linker scripts */ diff --git a/arch/s390/boot/startup.c b/arch/s390/boot/startup.c index 1aa11a8f57dd..7bb0d88db5c6 100644 --- a/arch/s390/boot/startup.c +++ b/arch/s390/boot/startup.c @@ -88,6 +88,11 @@ static void handle_relocs(unsigned long offset) dynsym = (Elf64_Sym *) vmlinux.dynsym_start; for (rela = rela_start; rela < rela_end; rela++) { loc = rela->r_offset + offset; + if ((loc >= vmlinux.start_mcount_loc) && + (loc < vmlinux.stop_mcount_loc)) { + (*(unsigned long *)loc) += offset; + continue; + } val = rela->r_addend; r_sym = ELF64_R_SYM(rela->r_info); if (r_sym) { @@ -232,6 +237,8 @@ static void offset_vmlinux_info(unsigned long offset) vmlinux.rela_dyn_start += offset; vmlinux.rela_dyn_end += offset; vmlinux.dynsym_start += offset; + vmlinux.start_mcount_loc += offset; + vmlinux.stop_mcount_loc += offset; } static unsigned long reserve_amode31(unsigned long safe_addr) diff --git a/arch/s390/kernel/vmlinux.lds.S b/arch/s390/kernel/vmlinux.lds.S index 42c43521878f..51c773405608 100644 --- a/arch/s390/kernel/vmlinux.lds.S +++ b/arch/s390/kernel/vmlinux.lds.S @@ -213,6 +213,8 @@ SECTIONS QUAD(__rela_dyn_start) /* rela_dyn_start */ QUAD(__rela_dyn_end) /* rela_dyn_end */ QUAD(_eamode31 - _samode31) /* amode31_size */ + QUAD(__start_mcount_loc) + QUAD(__stop_mcount_loc) } :NONE /* Debugging sections. */ Not sure whether that would also work on power, and also not sure whether i missed something thinking about that. Maybe it doesn't even work. ;-)
WARNING: multiple messages have this Message-ID (diff)
From: Sven Schnelle <svens@linux.ibm.com> To: Mark Rutland <mark.rutland@arm.com> Cc: keescook@chromium.org, hca@linux.ibm.com, linux-kernel@vger.kernel.org, Steven Rostedt <rostedt@goodmis.org>, Sachin Sant <sachinp@linux.ibm.com>, Yinan Liu <yinan@linux.alibaba.com>, linuxppc-dev@lists.ozlabs.org, ardb@kernel.org Subject: Re: [powerpc] ftrace warning kernel/trace/ftrace.c:2068 with code-patching selftests Date: Thu, 27 Jan 2022 14:16:31 +0100 [thread overview] Message-ID: <yt9dsft9gvyo.fsf@linux.ibm.com> (raw) In-Reply-To: <YfKZXvB9vCN1bA1c@FVFF77S0Q05N> (Mark Rutland's message of "Thu, 27 Jan 2022 13:08:46 +0000") Mark Rutland <mark.rutland@arm.com> writes: > On Thu, Jan 27, 2022 at 07:46:01AM -0500, Steven Rostedt wrote: >> On Thu, 27 Jan 2022 12:27:04 +0000 >> Mark Rutland <mark.rutland@arm.com> wrote: >> >> > Ah, so those non-ELF relocations for the mcount_loc table just mean "apply the >> > KASLR offset here", which is equivalent for all entries. >> > >> > That makes sense, thanks! >> >> And this is why we were having such a hard time understanding each other ;-) > > ;) > > With that in mind, I think that we understand that the build-time sort works > for: > > * arch/x86, becuase the non-ELF relocations for mcount_loc happen to be > equivalent. > > * arch/arm, because there's no dynamic relocaiton and the mcount_loc entries > have been finalized prior to sorting. > > ... but doesn't work for anyone else (including arm64) because the ELF > relocations are not equivalent, and need special care that is not yet > implemented. For s390 my idea is to just skip the addresses between __start_mcount_loc and __stop_mcount_loc, because for these addresses we know that they are 64 bits wide, so we just need to add the KASLR offset. I'm thinking about something like this: diff --git a/arch/s390/boot/compressed/decompressor.h b/arch/s390/boot/compressed/decompressor.h index f75cc31a77dd..015d7e2e94ef 100644 --- a/arch/s390/boot/compressed/decompressor.h +++ b/arch/s390/boot/compressed/decompressor.h @@ -25,6 +25,8 @@ struct vmlinux_info { unsigned long rela_dyn_start; unsigned long rela_dyn_end; unsigned long amode31_size; + unsigned long start_mcount_loc; + unsigned long stop_mcount_loc; }; /* Symbols defined by linker scripts */ diff --git a/arch/s390/boot/startup.c b/arch/s390/boot/startup.c index 1aa11a8f57dd..7bb0d88db5c6 100644 --- a/arch/s390/boot/startup.c +++ b/arch/s390/boot/startup.c @@ -88,6 +88,11 @@ static void handle_relocs(unsigned long offset) dynsym = (Elf64_Sym *) vmlinux.dynsym_start; for (rela = rela_start; rela < rela_end; rela++) { loc = rela->r_offset + offset; + if ((loc >= vmlinux.start_mcount_loc) && + (loc < vmlinux.stop_mcount_loc)) { + (*(unsigned long *)loc) += offset; + continue; + } val = rela->r_addend; r_sym = ELF64_R_SYM(rela->r_info); if (r_sym) { @@ -232,6 +237,8 @@ static void offset_vmlinux_info(unsigned long offset) vmlinux.rela_dyn_start += offset; vmlinux.rela_dyn_end += offset; vmlinux.dynsym_start += offset; + vmlinux.start_mcount_loc += offset; + vmlinux.stop_mcount_loc += offset; } static unsigned long reserve_amode31(unsigned long safe_addr) diff --git a/arch/s390/kernel/vmlinux.lds.S b/arch/s390/kernel/vmlinux.lds.S index 42c43521878f..51c773405608 100644 --- a/arch/s390/kernel/vmlinux.lds.S +++ b/arch/s390/kernel/vmlinux.lds.S @@ -213,6 +213,8 @@ SECTIONS QUAD(__rela_dyn_start) /* rela_dyn_start */ QUAD(__rela_dyn_end) /* rela_dyn_end */ QUAD(_eamode31 - _samode31) /* amode31_size */ + QUAD(__start_mcount_loc) + QUAD(__stop_mcount_loc) } :NONE /* Debugging sections. */ Not sure whether that would also work on power, and also not sure whether i missed something thinking about that. Maybe it doesn't even work. ;-)
next prev parent reply other threads:[~2022-01-27 13:17 UTC|newest] Thread overview: 46+ messages / expand[flat|nested] mbox.gz Atom feed top 2022-01-24 9:19 [powerpc] ftrace warning kernel/trace/ftrace.c:2068 with code-patching selftests Sachin Sant 2022-01-24 9:19 ` Sachin Sant 2022-01-24 12:15 ` Yinan Liu 2022-01-24 16:45 ` Steven Rostedt 2022-01-25 3:20 ` Yinan Liu 2022-01-26 14:37 ` Mark Rutland 2022-01-27 11:46 ` Mark Rutland 2022-01-27 11:46 ` Mark Rutland 2022-01-27 12:03 ` Ard Biesheuvel 2022-01-27 12:03 ` Ard Biesheuvel 2022-01-27 12:20 ` Mark Rutland 2022-01-27 12:20 ` Mark Rutland 2022-01-27 12:22 ` Ard Biesheuvel 2022-01-27 12:22 ` Ard Biesheuvel 2022-01-27 12:59 ` Mark Rutland 2022-01-27 12:59 ` Mark Rutland 2022-01-27 13:07 ` Ard Biesheuvel 2022-01-27 13:07 ` Ard Biesheuvel 2022-01-27 13:24 ` Mark Rutland 2022-01-27 13:24 ` Mark Rutland 2022-01-27 13:59 ` Ard Biesheuvel 2022-01-27 13:59 ` Ard Biesheuvel 2022-01-27 14:54 ` Mark Rutland 2022-01-27 14:54 ` Mark Rutland 2022-01-27 15:01 ` Ard Biesheuvel 2022-01-27 15:01 ` Ard Biesheuvel 2022-01-27 12:04 ` Sven Schnelle 2022-01-27 12:04 ` Sven Schnelle 2022-01-27 12:27 ` Mark Rutland 2022-01-27 12:27 ` Mark Rutland 2022-01-27 12:46 ` Steven Rostedt 2022-01-27 12:46 ` Steven Rostedt 2022-01-27 13:08 ` Mark Rutland 2022-01-27 13:08 ` Mark Rutland 2022-01-27 13:16 ` Sven Schnelle [this message] 2022-01-27 13:16 ` Sven Schnelle 2022-01-27 13:33 ` Mark Rutland 2022-01-27 13:33 ` Mark Rutland 2022-01-27 13:55 ` Steven Rostedt 2022-01-27 13:55 ` Steven Rostedt 2022-01-27 14:56 ` Mark Rutland 2022-01-27 14:56 ` Mark Rutland 2022-01-27 16:41 ` Kees Cook 2022-01-27 16:41 ` Kees Cook 2022-01-25 4:00 ` Sachin Sant 2022-01-25 14:28 ` Steven Rostedt
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