[PATCH 0/9] x86/kexec: Fixes for tip/x86/boot

[David Woodhouse]

On 16 December 2024 23:24:07 GMT, David Woodhouse <dwmw2 at infradead.org> wrote:
>Fix a few bugs introduced by the recent rework of the relocate_kernel()
>code, and one which has been there in the kjump code from the beginning.
>
> • Global read-only TLB entries made relocate_kernel() crash when writing
>   to its own page after the %cr3 switch should have made it writeable.
> • The preserve_context flag was lost when invoking swap_pages on the way
>   back, causing pages not to be swapped.
> • The wrong page was being used as the swap page.
> • The ABI for the kjump call asks the callee to put its entry address for
>   next time at %rsp+8 before returning, but we set %rsp to the top of the
>   available page, such that the entry address is at the start of some
>   other page.
> • The relocate_kernel() function lacked Clang CFI information, but is now
>   called via a function pointer, leading to a crash¹.
> • The relocate_kernel() code and data could end up being linked into the
>   wrong place for a LTO / -ffunction-sections build.
>
>Thanks to Nathan for reporting many of the above.
>
>Also a few minor cleanups, including a comments-only patch from Rafael 
>on the suspend-like part of kjump as a prelude to actually cleaning that 
>up.
>
>¹ Fixed by just adding __nocfi. Actually providing the CFI information 
>for relocate_kernel() will need a bit more work, so let's just do the 
>simple fix for now.
>
>David Woodhouse (7):
>      x86/kexec: Disable global pages before writing to control page
>      x86/kexec: Ensure preserve_context flag is set on return to kernel
>      x86/kexec: Use correct swap page in swap_pages function
>      x86/kexec: Fix stack and handling of re-entry point for ::preserve_context
>      x86/kexec: Mark machine_kexec() with __nocfi
>      x86/kexec: Cope with relocate_kernel() not being at the start of the page
>      x86/kexec: Use typedef for relocate_kernel_fn function prototype
>
>Nathan Chancellor (1):
>      x86/kexec: Fix location of relocate_kernel with -ffunction-sections
>
>Rafael J. Wysocki (1):
>      kexec_core: Add and update comments regarding the KEXEC_JUMP flow
>
> arch/x86/include/asm/kexec.h         | 26 ++++++++--------
> arch/x86/kernel/machine_kexec_32.c   |  7 +----
> arch/x86/kernel/machine_kexec_64.c   |  8 ++---
> arch/x86/kernel/relocate_kernel_64.S | 57 ++++++++++++++++++++++++------------
> arch/x86/kernel/vmlinux.lds.S        |  4 +--
> kernel/kexec_core.c                  | 23 +++++++++++----
> 6 files changed, 74 insertions(+), 51 deletions(-)
>
>

Ping? I made sure I got this series out quickly as it deals with regressions in tip/x86/boot. Aside from potentially being able to save a byte on one instruction, I think the rest of the discussion has been resolved without changing the patches.

I'll resend the follow-on parts which add the debugging support when I'm back at a real keyboard.