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x86/entry/64: Use JMP instead of JMPQ

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commit 64dbc122b20f75183d8822618c24f85144a5a94d upstream.

Somehow the swapgs mitigation entry code patch ended up with a JMPQ
instruction instead of JMP, where only the short jump is needed.  Some
assembler versions apparently fail to optimize JMPQ into a two-byte JMP
when possible, instead always using a 7-byte JMP with relocation.  For
some reason that makes the entry code explode with a #GP during boot.

Change it back to "JMP" as originally intended.

Fixes: 18ec54fdd6d1 ("x86/speculation: Prepare entry code for Spectre v1 swapgs mitigations")
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
[bwh: Backported to 4.4: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Josh Poimboeuf 2019-07-15 11:51:39 -05:00 • committed by Greg Kroah-Hartman
parent 73e2c1bd27
commit 967858f2f2
1 changed files with 1 additions and 1 deletions
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2
arch/x86/entry/entry_64.S
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@ -567,7 +567,7 @@ END(irq_entries_start)
#ifdef CONFIG_CONTEXT_TRACKING
call enter_from_user_mode
#endif
jmpq 2f
jmp 2f
1:
FENCE_SWAPGS_KERNEL_ENTRY
2: