kernel.git/arch/x86/kernel/vmlinux.lds.S, branch linux-4.14.y

x86: Fix .brk attribute in linker script

2023-11-08T10:21:08Z

commit 7e09ac27f43b382f5fe9bb7c7f4c465ece1f8a23 upstream. Commit in Fixes added the "NOLOAD" attribute to the .brk section as a "failsafe" measure. Unfortunately, this leads to the linker no longer covering the .brk section in a program header, resulting in the kernel loader not knowing that the memory for the .brk section must be reserved. This has led to crashes when loading the kernel as PV dom0 under Xen, but other scenarios could be hit by the same problem (e.g. in case an uncompressed kernel is used and the initrd is placed directly behind it). So drop the "NOLOAD" attribute. This has been verified to correctly cover the .brk section by a program header of the resulting ELF file. Fixes: e32683c6f7d2 ("x86/mm: Fix RESERVE_BRK() for older binutils") Signed-off-by: Juergen Gross Signed-off-by: Borislav Petkov Reviewed-by: Josh Poimboeuf Link: https://lore.kernel.org/r/20220630071441.28576-4-jgross@suse.com Signed-off-by: Greg Kroah-Hartman

x86/mm: Fix RESERVE_BRK() for older binutils

2023-11-08T10:21:07Z

commit e32683c6f7d22ba624e0bfc58b02cf3348bdca63 upstream. With binutils 2.26, RESERVE_BRK() causes a build failure: /tmp/ccnGOKZ5.s: Assembler messages: /tmp/ccnGOKZ5.s:98: Error: missing ')' /tmp/ccnGOKZ5.s:98: Error: missing ')' /tmp/ccnGOKZ5.s:98: Error: missing ')' /tmp/ccnGOKZ5.s:98: Error: junk at end of line, first unrecognized character is `U' The problem is this line: RESERVE_BRK(early_pgt_alloc, INIT_PGT_BUF_SIZE) Specifically, the INIT_PGT_BUF_SIZE macro which (via PAGE_SIZE's use _AC()) has a "1UL", which makes older versions of the assembler unhappy. Unfortunately the _AC() macro doesn't work for inline asm. Inline asm was only needed here to convince the toolchain to add the STT_NOBITS flag. However, if a C variable is placed in a section whose name is prefixed with ".bss", GCC and Clang automatically set STT_NOBITS. In fact, ".bss..page_aligned" already relies on this trick. So fix the build failure (and simplify the macro) by allocating the variable in C. Also, add NOLOAD to the ".brk" output section clause in the linker script. This is a failsafe in case the ".bss" prefix magic trick ever stops working somehow. If there's a section type mismatch, the GNU linker will force the ".brk" output section to be STT_NOBITS. The LLVM linker will fail with a "section type mismatch" error. Note this also changes the name of the variable from .brk.##name to __brk_##name. The variable names aren't actually used anywhere, so it's harmless. Fixes: a1e2c031ec39 ("x86/mm: Simplify RESERVE_BRK()") Reported-by: Joe Damato Reported-by: Byungchul Park Signed-off-by: Josh Poimboeuf Signed-off-by: Peter Zijlstra (Intel) Tested-by: Joe Damato Link: https://lore.kernel.org/r/22d07a44c80d8e8e1e82b9a806ddc8c6bbb2606e.1654759036.git.jpoimboe@kernel.org [nathan: Fix conflict due to lack of 360db4ace311 and resolve silent conflict with 360db4ace3117] Signed-off-by: Nathan Chancellor Signed-off-by: Greg Kroah-Hartman

x86, vmlinux.lds: Page-align end of ..page_aligned sections

2020-08-05T08:06:49Z

[ Upstream commit de2b41be8fcccb2f5b6c480d35df590476344201 ] On x86-32 the idt_table with 256 entries needs only 2048 bytes. It is page-aligned, but the end of the .bss..page_aligned section is not guaranteed to be page-aligned. As a result, objects from other .bss sections may end up on the same 4k page as the idt_table, and will accidentially get mapped read-only during boot, causing unexpected page-faults when the kernel writes to them. This could be worked around by making the objects in the page aligned sections page sized, but that's wrong. Explicit sections which store only page aligned objects have an implicit guarantee that the object is alone in the page in which it is placed. That works for all objects except the last one. That's inconsistent. Enforcing page sized objects for these sections would wreckage memory sanitizers, because the object becomes artificially larger than it should be and out of bound access becomes legit. Align the end of the .bss..page_aligned and .data..page_aligned section on page-size so all objects places in these sections are guaranteed to have their own page. [ tglx: Amended changelog ] Signed-off-by: Joerg Roedel Signed-off-by: Thomas Gleixner Reviewed-by: Kees Cook Cc: stable@vger.kernel.org Link: https://lkml.kernel.org/r/20200721093448.10417-1-joro@8bytes.org Signed-off-by: Sasha Levin

x86/build/lto: Fix truncated .bss with -fdata-sections

2020-08-05T08:06:49Z

[ Upstream commit 6a03469a1edc94da52b65478f1e00837add869a3 ] With CONFIG_LD_DEAD_CODE_DATA_ELIMINATION=y, we compile the kernel with -fdata-sections, which also splits the .bss section. The new section, with a new .bss.* name, which pattern gets missed by the main x86 linker script which only expects the '.bss' name. This results in the discarding of the second part and a too small, truncated .bss section and an unhappy, non-working kernel. Use the common BSS_MAIN macro in the linker script to properly capture and merge all the generated BSS sections. Signed-off-by: Sami Tolvanen Reviewed-by: Nick Desaulniers Reviewed-by: Kees Cook Cc: Borislav Petkov Cc: Kees Cook Cc: Linus Torvalds Cc: Nicholas Piggin Cc: Nick Desaulniers Cc: Peter Zijlstra Cc: Thomas Gleixner Link: http://lkml.kernel.org/r/20190415164956.124067-1-samitolvanen@google.com [ Extended the changelog. ] Signed-off-by: Ingo Molnar Signed-off-by: Sasha Levin

x86_64: Fix jiffies ODR violation

2020-06-20T08:25:00Z

commit d8ad6d39c35d2b44b3d48b787df7f3359381dcbf upstream. 'jiffies' and 'jiffies_64' are meant to alias (two different symbols that share the same address). Most architectures make the symbols alias to the same address via a linker script assignment in their arch//kernel/vmlinux.lds.S: jiffies = jiffies_64; which is effectively a definition of jiffies. jiffies and jiffies_64 are both forward declared for all architectures in include/linux/jiffies.h. jiffies_64 is defined in kernel/time/timer.c. x86_64 was peculiar in that it wasn't doing the above linker script assignment, but rather was: 1. defining jiffies in arch/x86/kernel/time.c instead via the linker script. 2. overriding the symbol jiffies_64 from kernel/time/timer.c in arch/x86/kernel/vmlinux.lds.s via 'jiffies_64 = jiffies;'. As Fangrui notes: In LLD, symbol assignments in linker scripts override definitions in object files. GNU ld appears to have the same behavior. It would probably make sense for LLD to error "duplicate symbol" but GNU ld is unlikely to adopt for compatibility reasons. This results in an ODR violation (UB), which seems to have survived thus far. Where it becomes harmful is when; 1. -fno-semantic-interposition is used: As Fangrui notes: Clang after LLVM commit 5b22bcc2b70d ("[X86][ELF] Prefer to lower MC_GlobalAddress operands to .Lfoo$local") defaults to -fno-semantic-interposition similar semantics which help -fpic/-fPIC code avoid GOT/PLT when the referenced symbol is defined within the same translation unit. Unlike GCC -fno-semantic-interposition, Clang emits such relocations referencing local symbols for non-pic code as well. This causes references to jiffies to refer to '.Ljiffies$local' when jiffies is defined in the same translation unit. Likewise, references to jiffies_64 become references to '.Ljiffies_64$local' in translation units that define jiffies_64. Because these differ from the names used in the linker script, they will not be rewritten to alias one another. 2. Full LTO Full LTO effectively treats all source files as one translation unit, causing these local references to be produced everywhere. When the linker processes the linker script, there are no longer any references to jiffies_64' anywhere to replace with 'jiffies'. And thus '.Ljiffies$local' and '.Ljiffies_64$local' no longer alias at all. In the process of porting patches enabling Full LTO from arm64 to x86_64, spooky bugs have been observed where the kernel appeared to boot, but init doesn't get scheduled. Avoid the ODR violation by matching other architectures and define jiffies only by linker script. For -fno-semantic-interposition + Full LTO, there is no longer a global definition of jiffies for the compiler to produce a local symbol which the linker script won't ensure aliases to jiffies_64. Fixes: 40747ffa5aa8 ("asmlinkage: Make jiffies visible") Reported-by: Nathan Chancellor Reported-by: Alistair Delva Debugged-by: Nick Desaulniers Debugged-by: Sami Tolvanen Suggested-by: Fangrui Song Signed-off-by: Bob Haarman Signed-off-by: Thomas Gleixner Tested-by: Sedat Dilek # build+boot on Reviewed-by: Andi Kleen Reviewed-by: Josh Poimboeuf Cc: stable@vger.kernel.org Link: https://github.com/ClangBuiltLinux/linux/issues/852 Link: https://lkml.kernel.org/r/20200602193100.229287-1-inglorion@google.com Signed-off-by: Greg Kroah-Hartman

Revert "x86/build: Move _etext to actual end of .text"

2019-06-09T07:18:20Z

This reverts commit 392bef709659abea614abfe53cf228e7a59876a4. It seems to cause lots of problems when using the gold linker, and no one really needs this at the moment, so just revert it from the stable trees. Cc: Sami Tolvanen Reported-by: Kees Cook Cc: Borislav Petkov Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Reported-by: Alec Ari Cc: Ingo Molnar Signed-off-by: Greg Kroah-Hartman

x86/build: Move _etext to actual end of .text

2019-05-31T13:47:23Z

[ Upstream commit 392bef709659abea614abfe53cf228e7a59876a4 ] When building x86 with Clang LTO and CFI, CFI jump regions are automatically added to the end of the .text section late in linking. As a result, the _etext position was being labelled before the appended jump regions, causing confusion about where the boundaries of the executable region actually are in the running kernel, and broke at least the fault injection code. This moves the _etext mark to outside (and immediately after) the .text area, as it already the case on other architectures (e.g. arm64, arm). Reported-and-tested-by: Sami Tolvanen Signed-off-by: Kees Cook Cc: Borislav Petkov Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Link: http://lkml.kernel.org/r/20190423183827.GA4012@beast Signed-off-by: Ingo Molnar Signed-off-by: Sasha Levin

x86/build: Mark per-CPU symbols as absolute explicitly for LLD

2019-04-05T20:31:40Z

[ Upstream commit d071ae09a4a1414c1433d5ae9908959a7325b0ad ] Accessing per-CPU variables is done by finding the offset of the variable in the per-CPU block and adding it to the address of the respective CPU's block. Section 3.10.8 of ld.bfd's documentation states: For expressions involving numbers, relative addresses and absolute addresses, ld follows these rules to evaluate terms: Other binary operations, that is, between two relative addresses not in the same section, or between a relative address and an absolute address, first convert any non-absolute term to an absolute address before applying the operator." Note that LLVM's linker does not adhere to the GNU ld's implementation and as such requires implicitly-absolute terms to be explicitly marked as absolute in the linker script. If not, it fails currently with: ld.lld: error: ./arch/x86/kernel/vmlinux.lds:153: at least one side of the expression must be absolute ld.lld: error: ./arch/x86/kernel/vmlinux.lds:154: at least one side of the expression must be absolute Makefile:1040: recipe for target 'vmlinux' failed This is not a functional change for ld.bfd which converts the term to an absolute symbol anyways as specified above. Based on a previous submission by Tri Vo . Reported-by: Dmitry Golovin Signed-off-by: Rafael Ávila de Espíndola [ Update commit message per Boris' and Michael's suggestions. ] Signed-off-by: Nick Desaulniers [ Massage commit message more, fix typos. ] Signed-off-by: Borislav Petkov Tested-by: Dmitry Golovin Cc: "H. Peter Anvin" Cc: Andy Lutomirski Cc: Brijesh Singh Cc: Cao Jin Cc: Ingo Molnar Cc: Joerg Roedel Cc: Masahiro Yamada Cc: Masami Hiramatsu Cc: Thomas Gleixner Cc: Tri Vo Cc: dima@golovin.in Cc: morbo@google.com Cc: x86-ml Link: https://lkml.kernel.org/r/20181219190145.252035-1-ndesaulniers@google.com Signed-off-by: Sasha Levin

x86/kprobes: Fix kernel crash when probing .entry_trampoline code

2018-03-15T09:54:38Z

commit c07a8f8b08ba683ea24f3ac9159f37ae94daf47f upstream. Disable the kprobe probing of the entry trampoline: .entry_trampoline is a code area that is used to ensure page table isolation between userspace and kernelspace. At the beginning of the execution of the trampoline, we load the kernel's CR3 register. This has the effect of enabling the translation of the kernel virtual addresses to physical addresses. Before this happens most kernel addresses can not be translated because the running process' CR3 is still used. If a kprobe is placed on the trampoline code before that change of the CR3 register happens the kernel crashes because int3 handling pages are not accessible. To fix this, add the .entry_trampoline section to the kprobe blacklist to prohibit the probing of code before all the kernel pages are accessible. Signed-off-by: Francis Deslauriers Reviewed-by: Thomas Gleixner Cc: Andy Lutomirski Cc: Borislav Petkov Cc: Brian Gerst Cc: Denys Vlasenko Cc: H. Peter Anvin Cc: Josh Poimboeuf Cc: Linus Torvalds Cc: Peter Zijlstra Cc: mathieu.desnoyers@efficios.com Cc: mhiramat@kernel.org Link: http://lkml.kernel.org/r/1520565492-4637-2-git-send-email-francis.deslauriers@efficios.com Signed-off-by: Ingo Molnar Signed-off-by: Greg Kroah-Hartman

retpoline: Introduce start/end markers of indirect thunk

2018-01-23T18:58:20Z

commit 736e80a4213e9bbce40a7c050337047128b472ac upstream. Introduce start/end markers of __x86_indirect_thunk_* functions. To make it easy, consolidate .text.__x86.indirect_thunk.* sections to one .text.__x86.indirect_thunk section and put it in the end of kernel text section and adds __indirect_thunk_start/end so that other subsystem (e.g. kprobes) can identify it. Signed-off-by: Masami Hiramatsu Signed-off-by: Thomas Gleixner Acked-by: David Woodhouse Cc: Andi Kleen Cc: Peter Zijlstra Cc: Ananth N Mavinakayanahalli Cc: Arjan van de Ven Cc: Greg Kroah-Hartman Link: https://lkml.kernel.org/r/151629206178.10241.6828804696410044771.stgit@devbox Signed-off-by: Greg Kroah-Hartman