kernel.git/arch/x86/kernel/vmlinux.lds.S, branch linux-4.19.y

x86: Fix .brk attribute in linker script

2023-11-08T10:22:19Z

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

2023-11-08T10:22:18Z

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

2020-07-29T08:16:58Z

commit de2b41be8fcccb2f5b6c480d35df590476344201 upstream. 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: Greg Kroah-Hartman

x86_64: Fix jiffies ODR violation

2020-06-22T07:05:01Z

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"

2019-06-09T07:17:23Z

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

2019-05-31T13:46:16Z

[ 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/lto: Fix truncated .bss with -fdata-sections

2019-05-16T17:41:22Z

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

2019-04-05T20:33:16Z

[ 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/mm: Add .bss..decrypted section to hold shared variables

2018-09-15T18:48:45Z

kvmclock defines few static variables which are shared with the hypervisor during the kvmclock initialization. When SEV is active, memory is encrypted with a guest-specific key, and if the guest OS wants to share the memory region with the hypervisor then it must clear the C-bit before sharing it. Currently, we use kernel_physical_mapping_init() to split large pages before clearing the C-bit on shared pages. But it fails when called from the kvmclock initialization (mainly because the memblock allocator is not ready that early during boot). Add a __bss_decrypted section attribute which can be used when defining such shared variable. The so-defined variables will be placed in the .bss..decrypted section. This section will be mapped with C=0 early during boot. The .bss..decrypted section has a big chunk of memory that may be unused when memory encryption is not active, free it when memory encryption is not active. Suggested-by: Thomas Gleixner Signed-off-by: Brijesh Singh Signed-off-by: Thomas Gleixner Cc: Tom Lendacky Cc: Borislav Petkov Cc: "H. Peter Anvin" Cc: Paolo Bonzini Cc: Sean Christopherson Cc: Radim Krčmář Cc: kvm@vger.kernel.org Link: https://lkml.kernel.org/r/1536932759-12905-2-git-send-email-brijesh.singh@amd.com

x86/mm/pti: Make pti_clone_kernel_text() compile on 32 bit

2018-07-19T23:11:44Z

The pti_clone_kernel_text() function references __end_rodata_hpage_align, which is only present on x86-64. This makes sense as the end of the rodata section is not huge-page aligned on 32 bit. Nevertheless a symbol is required for the function that points at the right address for both 32 and 64 bit. Introduce __end_rodata_aligned for that purpose and use it in pti_clone_kernel_text(). Signed-off-by: Joerg Roedel Signed-off-by: Thomas Gleixner Tested-by: Pavel Machek Cc: "H . Peter Anvin" Cc: linux-mm@kvack.org Cc: Linus Torvalds Cc: Andy Lutomirski Cc: Dave Hansen Cc: Josh Poimboeuf Cc: Juergen Gross Cc: Peter Zijlstra Cc: Borislav Petkov Cc: Jiri Kosina Cc: Boris Ostrovsky Cc: Brian Gerst Cc: David Laight Cc: Denys Vlasenko Cc: Eduardo Valentin Cc: Greg KH Cc: Will Deacon Cc: aliguori@amazon.com Cc: daniel.gruss@iaik.tugraz.at Cc: hughd@google.com Cc: keescook@google.com Cc: Andrea Arcangeli Cc: Waiman Long Cc: "David H . Gutteridge" Cc: joro@8bytes.org Link: https://lkml.kernel.org/r/1531906876-13451-28-git-send-email-joro@8bytes.org