linux.git/arch/x86/include/asm/setup.h, branch v6.14

x86/boot/64: Determine VA/PA offset before entering C code

2024-12-05T12:18:54+00:00

Implicit absolute symbol references (e.g., taking the address of a
global variable) must be avoided in the C code that runs from the early
1:1 mapping of the kernel, given that this is a practice that violates
assumptions on the part of the toolchain. I.e., RIP-relative and
absolute references are expected to produce the same values, and so the
compiler is free to choose either. However, the code currently assumes
that RIP-relative references are never emitted here.

So an explicit virtual-to-physical offset needs to be used instead to
derive the kernel virtual addresses of _text and _end, instead of simply
taking the addresses and assuming that the compiler will not choose to
use a RIP-relative references in this particular case.

Currently, phys_base is already used to perform such calculations, but
it is derived from the kernel virtual address of _text, which is taken
using an implicit absolute symbol reference. So instead, derive this
VA-to-PA offset in asm code, and pass it to the C startup code.

Signed-off-by: Ard Biesheuvel 
Signed-off-by: Ingo Molnar 
Cc: Linus Torvalds 
Cc: "H. Peter Anvin" 
Link: https://lore.kernel.org/r/20241205112804.3416920-11-ardb+git@google.com

x86/setup: Warn when option parsing is done too early

2024-05-27T16:54:45+00:00

Commit

  4faa0e5d6d79 ("x86/boot: Move kernel cmdline setup earlier in the boot process (again)")

fixed and issue where cmdline parsing would happen before the final
boot_command_line string has been built from the builtin and boot
cmdlines and thus cmdline arguments would get lost.

Add a check to catch any future wrong use ordering so that such issues
can be caught in time.

Signed-off-by: Borislav Petkov (AMD) 
Acked-by: Ingo Molnar 
Link: https://lore.kernel.org/r/20240409152541.GCZhVd9XIPXyTNd9vc@fat_crate.local

x86/boot/64: Simplify global variable accesses in GDT/IDT programming

2024-02-26T11:58:11+00:00

There are two code paths in the startup code to program an IDT: one that
runs from the 1:1 mapping and one that runs from the virtual kernel
mapping. Currently, these are strictly separate because fixup_pointer()
is used on the 1:1 path, which will produce the wrong value when used
while executing from the virtual kernel mapping.

Switch to RIP_REL_REF() so that the two code paths can be merged. Also,
move the GDT and IDT descriptors to the stack so that they can be
referenced directly, rather than via RIP_REL_REF().

Rename startup_64_setup_env() to startup_64_setup_gdt_idt() while at it,
to make the call from assembler self-documenting.

Signed-off-by: Ard Biesheuvel 
Signed-off-by: Borislav Petkov (AMD) 
Signed-off-by: Ard Biesheuvel 
Signed-off-by: Ingo Molnar 
Link: https://lore.kernel.org/r/20240221113506.2565718-19-ardb+git@google.com

x86/setup: Make relocated_ramdisk a local variable of relocate_initrd()

2023-11-13T08:09:37+00:00

After

  0b62f6cb0773 ("x86/microcode/32: Move early loading after paging enable"),

the global variable relocated_ramdisk is no longer used anywhere except
for the relocate_initrd() function. Make it a local variable of that
function.

Signed-off-by: Yuntao Wang 
Signed-off-by: Borislav Petkov (AMD) 
Reviewed-by: Baoquan He 
Link: https://lore.kernel.org/r/20231113034026.130679-1-ytcoode@gmail.com

x86/boot/32: De-uglify the 2/3 level paging difference in mk_early_pgtbl_32()

2023-10-18T16:27:30+00:00

Move the ifdeffery out of the function and use proper typedefs to make it
work for both 2 and 3 level paging.

No functional change.

  [ bp: Move mk_early_pgtbl_32() declaration into a header. ]

Signed-off-by: Thomas Gleixner 
Signed-off-by: Borislav Petkov (AMD) 
Link: https://lore.kernel.org/r/20231017211722.111059491@linutronix.de

x86/head: Mark *_start_kernel() __noreturn

2023-04-14T15:31:24+00:00

Now that start_kernel() is __noreturn, mark its chain of callers
__noreturn.

Signed-off-by: Josh Poimboeuf 
Signed-off-by: Peter Zijlstra (Intel) 
Link: https://lore.kernel.org/r/c2525f96b88be98ee027ee0291d58003036d4120.1681342859.git.jpoimboe@kernel.org

x86/xen: Use clear_bss() for Xen PV guests

2022-07-01T08:57:52+00:00

Instead of clearing the bss area in assembly code, use the clear_bss()
function.

This requires to pass the start_info address as parameter to
xen_start_kernel() in order to avoid the xen_start_info being zeroed
again.

Signed-off-by: Juergen Gross 
Signed-off-by: Borislav Petkov 
Reviewed-by: Jan Beulich 
Reviewed-by: Boris Ostrovsky 
Link: https://lore.kernel.org/r/20220630071441.28576-2-jgross@suse.com

x86/mm: Fix RESERVE_BRK() for older binutils

2022-06-13T08:15:04+00:00

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

Merge tag 'x86_asm_for_v5.19_rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

2022-05-24T01:08:46+00:00

Pull x86 asm updates from Borislav Petkov:

 - A bunch of changes towards streamlining low level asm helpers'
   calling conventions so that former can be converted to C eventually

 - Simplify PUSH_AND_CLEAR_REGS so that it can be used at the system
   call entry paths instead of having opencoded, slightly different
   variants of it everywhere

 - Misc other fixes

* tag 'x86_asm_for_v5.19_rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  x86/entry: Fix register corruption in compat syscall
  objtool: Fix STACK_FRAME_NON_STANDARD reloc type
  linkage: Fix issue with missing symbol size
  x86/entry: Remove skip_r11rcx
  x86/entry: Use PUSH_AND_CLEAR_REGS for compat
  x86/entry: Simplify entry_INT80_compat()
  x86/mm: Simplify RESERVE_BRK()
  x86/entry: Convert SWAPGS to swapgs and remove the definition of SWAPGS
  x86/entry: Don't call error_entry() for XENPV
  x86/entry: Move CLD to the start of the idtentry macro
  x86/entry: Move PUSH_AND_CLEAR_REGS out of error_entry()
  x86/entry: Switch the stack after error_entry() returns
  x86/traps: Use pt_regs directly in fixup_bad_iret()

x86/mm: Simplify RESERVE_BRK()

2022-05-06T13:26:33+00:00

RESERVE_BRK() reserves data in the .brk_reservation section.  The data
is initialized to zero, like BSS, so the macro specifies 'nobits' to
prevent the data from taking up space in the vmlinux binary.  The only
way to get the compiler to do that (without putting the variable in .bss
proper) is to use inline asm.

The macro also has a hack which encloses the inline asm in a discarded
function, which allows the size to be passed (global inline asm doesn't
allow inputs).

Remove the need for the discarded function hack by just stringifying the
size rather than supplying it as an input to the inline asm.

Signed-off-by: Josh Poimboeuf 
Signed-off-by: Peter Zijlstra (Intel) 
Signed-off-by: Borislav Petkov 
Reviewed-by: Borislav Petkov 
Link: https://lore.kernel.org/r/20220506121631.133110232@infradead.org