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x86/boot/compressed/64: Set up GOT for paging_prepare() and cleanup_trampoline()

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Eric and Hugh have reported instant reboot due to my recent changes in
decompression code.

The root cause is that I didn't realize that we need to adjust GOT to be
able to run C code that early.

The problem is only visible with an older toolchain. Binutils >= 2.24 is
able to eliminate GOT references by replacing them with RIP-relative
address loads:

  https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;a=commitdiff;h=80d873266dec

We need to adjust GOT two times:

 - before calling paging_prepare() using the initial load address
 - before calling C code from the relocated kernel

Reported-by: Eric Dumazet <eric.dumazet@gmail.com>
Reported-by: Hugh Dickins <hughd@google.com>
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Fixes: 194a9749c7 ("x86/boot/compressed/64: Handle 5-level paging boot if kernel is above 4G")
Link: http://lkml.kernel.org/r/20180516080131.27913-2-kirill.shutemov@linux.intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Kirill A. Shutemov 2018-05-16 11:01:28 +03:00 committed by Ingo Molnar
parent 2fa9d1cfaf
commit 5c9b0b1c49
1 changed files with 55 additions and 13 deletions
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68
arch/x86/boot/compressed/head_64.S
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@ -305,6 +305,25 @@ ENTRY(startup_64)
/* Set up the stack */
leaq boot_stack_end(%rbx), %rsp
/*
* paging_prepare() and cleanup_trampoline() below can have GOT
* references. Adjust the table with address we are running at.
*
* Zero RAX for adjust_got: the GOT was not adjusted before;
* there's no adjustment to undo.
*/
xorq %rax, %rax
/*
* Calculate the address the binary is loaded at and use it as
* a GOT adjustment.
*/
call 1f
1: popq %rdi
subq $1b, %rdi
call adjust_got
/*
* At this point we are in long mode with 4-level paging enabled,
* but we might want to enable 5-level paging or vice versa.
@ -381,6 +400,21 @@ trampoline_return:
pushq $0
popfq
/*
* Previously we've adjusted the GOT with address the binary was
* loaded at. Now we need to re-adjust for relocation address.
*
* Calculate the address the binary is loaded at, so that we can
* undo the previous GOT adjustment.
*/
call 1f
1: popq %rax
subq $1b, %rax
/* The new adjustment is the relocation address */
movq %rbx, %rdi
call adjust_got
/*
* Copy the compressed kernel to the end of our buffer
* where decompression in place becomes safe.
@ -481,19 +515,6 @@ relocated:
shrq $3, %rcx
rep stosq
/*
* Adjust our own GOT
*/
leaq _got(%rip), %rdx
leaq _egot(%rip), %rcx
1:
cmpq %rcx, %rdx
jae 2f
addq %rbx, (%rdx)
addq $8, %rdx
jmp 1b
2:
/*
* Do the extraction, and jump to the new kernel..
*/
@ -512,6 +533,27 @@ relocated:
*/
jmp *%rax
/*
* Adjust the global offset table
*
* RAX is the previous adjustment of the table to undo (use 0 if it's the
* first time we touch GOT).
* RDI is the new adjustment to apply.
*/
adjust_got:
/* Walk through the GOT adding the address to the entries */
leaq _got(%rip), %rdx
leaq _egot(%rip), %rcx
1:
cmpq %rcx, %rdx
jae 2f
subq %rax, (%rdx) /* Undo previous adjustment */
addq %rdi, (%rdx) /* Apply the new adjustment */
addq $8, %rdx
jmp 1b
2:
ret
.code32
/*
* This is the 32-bit trampoline that will be copied over to low memory.