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s390: extend expoline to BC instructions

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The BPF JIT uses a 'b <disp>(%r<x>)' instruction in the definition
of the sk_load_word and sk_load_half functions.

Add support for branch-on-condition instructions contained in the
thunk code of an expoline.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
This commit is contained in:
Martin Schwidefsky
2018-04-24 15:32:08 +02:00
parent 9f18fff63c
commit 6deaa3bbca
2 changed files with 77 additions and 5 deletions
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25
arch/s390/kernel/nospec-branch.c
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@@ -93,7 +93,6 @@ static void __init_or_module __nospec_revert(s32 *start, s32 *end)
s32 *epo;
/* Second part of the instruction replace is always a nop */
memcpy(insnbuf + 2, (char[]) { 0x47, 0x00, 0x00, 0x00 }, 4);
for (epo = start; epo < end; epo++) {
instr = (u8 *) epo + *epo;
if (instr[0] == 0xc0 && (instr[1] & 0x0f) == 0x04)
@@ -114,18 +113,34 @@ static void __init_or_module __nospec_revert(s32 *start, s32 *end)
br = thunk + (*(int *)(thunk + 2)) * 2;
else
continue;
if (br[0] != 0x07 || (br[1] & 0xf0) != 0xf0)
/* Check for unconditional branch 0x07f? or 0x47f???? */
if ((br[0] & 0xbf) != 0x07 || (br[1] & 0xf0) != 0xf0)
continue;
memcpy(insnbuf + 2, (char[]) { 0x47, 0x00, 0x07, 0x00 }, 4);
switch (type) {
case BRCL_EXPOLINE:
/* brcl to thunk, replace with br + nop */
insnbuf[0] = br[0];
insnbuf[1] = (instr[1] & 0xf0) | (br[1] & 0x0f);
if (br[0] == 0x47) {
/* brcl to b, replace with bc + nopr */
insnbuf[2] = br[2];
insnbuf[3] = br[3];
} else {
/* brcl to br, replace with bcr + nop */
}
break;
case BRASL_EXPOLINE:
/* brasl to thunk, replace with basr + nop */
insnbuf[0] = 0x0d;
insnbuf[1] = (instr[1] & 0xf0) | (br[1] & 0x0f);
if (br[0] == 0x47) {
/* brasl to b, replace with bas + nopr */
insnbuf[0] = 0x4d;
insnbuf[2] = br[2];
insnbuf[3] = br[3];
} else {
/* brasl to br, replace with basr + nop */
insnbuf[0] = 0x0d;
}
break;
}