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parisc: fix race condition in patching code 

Assume the following ftrace code sequence that was patched in earlier by
ftrace_make_call():

PAGE A:
ffc:	addr of ftrace_caller()
PAGE B:
000:	0x6fc10080 /* stw,ma r1,40(sp) */
004:	0x48213fd1 /* ldw -18(r1),r1 */
008:	0xe820c002 /* bv,n r0(r1) */
00c:	0xe83f1fdf /* b,l,n .-c,r1 */

When a Code sequences that is to be patched spans a page break, we might
have already cleared the part on the PAGE A. If an interrupt is coming in
during the remap of the fixed mapping to PAGE B, it might execute the
patched function with only parts of the FTRACE code cleared. To prevent
this, clear the jump to our mini trampoline first, and clear the remaining
parts after this. This might also happen when patch_text() patches a
function that it calls during remap.

Signed-off-by: Sven Schnelle <svens@stackframe.org>
Cc: <stable@vger.kernel.org> # 5.2+
Signed-off-by: Helge Deller <deller@gmx.de>
This commit is contained in:
Sven Schnelle 2019-07-23 22:37:54 +02:00 committed by Helge Deller
parent c5df04521b
commit 740f05f30a
1 changed files with 2 additions and 1 deletions
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3
arch/parisc/kernel/ftrace.c
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@ -181,8 +181,9 @@ int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec,
for (i = 0; i < ARRAY_SIZE(insn); i++)
insn[i] = INSN_NOP;
__patch_text((void *)rec->ip, INSN_NOP);
__patch_text_multiple((void *)rec->ip + 4 - sizeof(insn),
insn, sizeof(insn));
insn, sizeof(insn)-4);
return 0;
}
#endif