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authorKirill A. Shutemov <kirill.shutemov@linux.intel.com>2018-05-16 11:01:28 +0300
committerIngo Molnar <mingo@kernel.org>2018-05-16 12:15:13 +0200
commit5c9b0b1c49881c680d4a56b9d9e03dfb3160fd4d (patch)
tree42aa65ef4c13221b669153cd743c9346f9042b1a /arch
parent2fa9d1cfaf0e02f8abef0757002bff12dfcfa4e6 (diff)
downloadlinux-5c9b0b1c49881c680d4a56b9d9e03dfb3160fd4d.tar.bz2
x86/boot/compressed/64: Set up GOT for paging_prepare() and cleanup_trampoline()
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: 194a9749c73d ("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>
Diffstat (limited to 'arch')
-rw-r--r--arch/x86/boot/compressed/head_64.S68
1 files changed, 55 insertions, 13 deletions
diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S
index fca012baba19..d17af6a4bfc9 100644
--- a/arch/x86/boot/compressed/head_64.S
+++ b/arch/x86/boot/compressed/head_64.S
@@ -306,6 +306,25 @@ ENTRY(startup_64)
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.
@@ -482,19 +516,6 @@ relocated:
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..
*/
pushq %rsi /* Save the real mode argument */
@@ -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.