| Message ID | efabcfb022d29fb0a9ccb39380623573555c2bcb.1507128293.git.jpoimboe@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On 04/10/17 17:58, Josh Poimboeuf wrote: > Add alternative patching support for replacing an instruction with an > indirect call. This will be needed for the paravirt alternatives. > > Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com> > --- > arch/x86/kernel/alternative.c | 22 +++++++++++++++------- > 1 file changed, 15 insertions(+), 7 deletions(-) > > diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c > index 3344d3382e91..81c577c7deba 100644 > --- a/arch/x86/kernel/alternative.c > +++ b/arch/x86/kernel/alternative.c > @@ -410,20 +410,28 @@ void __init_or_module noinline apply_alternatives(struct alt_instr *start, > insnbuf_sz = a->replacementlen; > > /* > - * 0xe8 is a relative jump; fix the offset. > - * > - * Instruction length is checked before the opcode to avoid > - * accessing uninitialized bytes for zero-length replacements. > + * Fix the address offsets for call and jump instructions which > + * use PC-relative addressing. > */ > if (a->replacementlen == 5 && *insnbuf == 0xe8) { > + /* direct call */ > *(s32 *)(insnbuf + 1) += replacement - instr; > - DPRINTK("Fix CALL offset: 0x%x, CALL 0x%lx", > + DPRINTK("Fix direct CALL offset: 0x%x, CALL 0x%lx", > *(s32 *)(insnbuf + 1), > (unsigned long)instr + *(s32 *)(insnbuf + 1) + 5); > - } > > - if (a->replacementlen && is_jmp(replacement[0])) > + } else if (a->replacementlen == 6 && *insnbuf == 0xff && > + *(insnbuf+1) == 0x15) { > + /* indirect call */ > + *(s32 *)(insnbuf + 2) += replacement - instr; > + DPRINTK("Fix indirect CALL offset: 0x%x, CALL *0x%lx", > + *(s32 *)(insnbuf + 2), > + (unsigned long)instr + *(s32 *)(insnbuf + 2) + 6); > + > + } else if (a->replacementlen && is_jmp(replacement[0])) { Is this correct? Without your patch this was: if (*insnbuf == 0xe8) ... if (is_jmp(replacement[0])) ... Now you have: if (*insnbuf == 0xe8) ... else if (*insnbuf == 0xff15) ... else if (is_jmp(replacement[0])) ... So only one or none of the three variants will be executed. In the past it could be none, one or both. Juergen
On Wed, Oct 25, 2017 at 01:25:02PM +0200, Juergen Gross wrote: > On 04/10/17 17:58, Josh Poimboeuf wrote: > > Add alternative patching support for replacing an instruction with an > > indirect call. This will be needed for the paravirt alternatives. > > > > Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com> > > --- > > arch/x86/kernel/alternative.c | 22 +++++++++++++++------- > > 1 file changed, 15 insertions(+), 7 deletions(-) > > > > diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c > > index 3344d3382e91..81c577c7deba 100644 > > --- a/arch/x86/kernel/alternative.c > > +++ b/arch/x86/kernel/alternative.c > > @@ -410,20 +410,28 @@ void __init_or_module noinline apply_alternatives(struct alt_instr *start, > > insnbuf_sz = a->replacementlen; > > > > /* > > - * 0xe8 is a relative jump; fix the offset. > > - * > > - * Instruction length is checked before the opcode to avoid > > - * accessing uninitialized bytes for zero-length replacements. > > + * Fix the address offsets for call and jump instructions which > > + * use PC-relative addressing. > > */ > > if (a->replacementlen == 5 && *insnbuf == 0xe8) { > > + /* direct call */ > > *(s32 *)(insnbuf + 1) += replacement - instr; > > - DPRINTK("Fix CALL offset: 0x%x, CALL 0x%lx", > > + DPRINTK("Fix direct CALL offset: 0x%x, CALL 0x%lx", > > *(s32 *)(insnbuf + 1), > > (unsigned long)instr + *(s32 *)(insnbuf + 1) + 5); > > - } > > > > - if (a->replacementlen && is_jmp(replacement[0])) > > + } else if (a->replacementlen == 6 && *insnbuf == 0xff && > > + *(insnbuf+1) == 0x15) { > > + /* indirect call */ > > + *(s32 *)(insnbuf + 2) += replacement - instr; > > + DPRINTK("Fix indirect CALL offset: 0x%x, CALL *0x%lx", > > + *(s32 *)(insnbuf + 2), > > + (unsigned long)instr + *(s32 *)(insnbuf + 2) + 6); > > + > > + } else if (a->replacementlen && is_jmp(replacement[0])) { > > Is this correct? Without your patch this was: > > if (*insnbuf == 0xe8) ... > if (is_jmp(replacement[0])) ... > > Now you have: > > if (*insnbuf == 0xe8) ... > else if (*insnbuf == 0xff15) ... > else if (is_jmp(replacement[0])) ... > > So only one or none of the three variants will be executed. In the past > it could be none, one or both. It can't be a call *and* a jump. It's either one or the other. Maybe it's a little confusing that the jump check uses replacement[0] while the other checks use *insnbuf? They have the same value, so the same variable should probably be used everywhere for consistency. I can make them more consistent.
On 16/11/17 22:19, Josh Poimboeuf wrote: > On Wed, Oct 25, 2017 at 01:25:02PM +0200, Juergen Gross wrote: >> On 04/10/17 17:58, Josh Poimboeuf wrote: >>> Add alternative patching support for replacing an instruction with an >>> indirect call. This will be needed for the paravirt alternatives. >>> >>> Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com> >>> --- >>> arch/x86/kernel/alternative.c | 22 +++++++++++++++------- >>> 1 file changed, 15 insertions(+), 7 deletions(-) >>> >>> diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c >>> index 3344d3382e91..81c577c7deba 100644 >>> --- a/arch/x86/kernel/alternative.c >>> +++ b/arch/x86/kernel/alternative.c >>> @@ -410,20 +410,28 @@ void __init_or_module noinline apply_alternatives(struct alt_instr *start, >>> insnbuf_sz = a->replacementlen; >>> >>> /* >>> - * 0xe8 is a relative jump; fix the offset. >>> - * >>> - * Instruction length is checked before the opcode to avoid >>> - * accessing uninitialized bytes for zero-length replacements. >>> + * Fix the address offsets for call and jump instructions which >>> + * use PC-relative addressing. >>> */ >>> if (a->replacementlen == 5 && *insnbuf == 0xe8) { >>> + /* direct call */ >>> *(s32 *)(insnbuf + 1) += replacement - instr; >>> - DPRINTK("Fix CALL offset: 0x%x, CALL 0x%lx", >>> + DPRINTK("Fix direct CALL offset: 0x%x, CALL 0x%lx", >>> *(s32 *)(insnbuf + 1), >>> (unsigned long)instr + *(s32 *)(insnbuf + 1) + 5); >>> - } >>> >>> - if (a->replacementlen && is_jmp(replacement[0])) >>> + } else if (a->replacementlen == 6 && *insnbuf == 0xff && >>> + *(insnbuf+1) == 0x15) { >>> + /* indirect call */ >>> + *(s32 *)(insnbuf + 2) += replacement - instr; >>> + DPRINTK("Fix indirect CALL offset: 0x%x, CALL *0x%lx", >>> + *(s32 *)(insnbuf + 2), >>> + (unsigned long)instr + *(s32 *)(insnbuf + 2) + 6); >>> + >>> + } else if (a->replacementlen && is_jmp(replacement[0])) { >> >> Is this correct? Without your patch this was: >> >> if (*insnbuf == 0xe8) ... >> if (is_jmp(replacement[0])) ... >> >> Now you have: >> >> if (*insnbuf == 0xe8) ... >> else if (*insnbuf == 0xff15) ... >> else if (is_jmp(replacement[0])) ... >> >> So only one or none of the three variants will be executed. In the past >> it could be none, one or both. > > It can't be a call *and* a jump. It's either one or the other. > > Maybe it's a little confusing that the jump check uses replacement[0] > while the other checks use *insnbuf? They have the same value, so the Right, I was fooled by that. > same variable should probably be used everywhere for consistency. I can > make them more consistent. > I'd appreciate that. :-) Juergen
On 10/04/17 08:58, Josh Poimboeuf wrote: > Add alternative patching support for replacing an instruction with an > indirect call. This will be needed for the paravirt alternatives. I have a patchset that generalizes the alternatives in what I think is a more robust way. I really, really want to get rid of these hacks. Let me clean it up an post it... -hpa
diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c index 3344d3382e91..81c577c7deba 100644 --- a/arch/x86/kernel/alternative.c +++ b/arch/x86/kernel/alternative.c @@ -410,20 +410,28 @@ void __init_or_module noinline apply_alternatives(struct alt_instr *start, insnbuf_sz = a->replacementlen; /* - * 0xe8 is a relative jump; fix the offset. - * - * Instruction length is checked before the opcode to avoid - * accessing uninitialized bytes for zero-length replacements. + * Fix the address offsets for call and jump instructions which + * use PC-relative addressing. */ if (a->replacementlen == 5 && *insnbuf == 0xe8) { + /* direct call */ *(s32 *)(insnbuf + 1) += replacement - instr; - DPRINTK("Fix CALL offset: 0x%x, CALL 0x%lx", + DPRINTK("Fix direct CALL offset: 0x%x, CALL 0x%lx", *(s32 *)(insnbuf + 1), (unsigned long)instr + *(s32 *)(insnbuf + 1) + 5); - } - if (a->replacementlen && is_jmp(replacement[0])) + } else if (a->replacementlen == 6 && *insnbuf == 0xff && + *(insnbuf+1) == 0x15) { + /* indirect call */ + *(s32 *)(insnbuf + 2) += replacement - instr; + DPRINTK("Fix indirect CALL offset: 0x%x, CALL *0x%lx", + *(s32 *)(insnbuf + 2), + (unsigned long)instr + *(s32 *)(insnbuf + 2) + 6); + + } else if (a->replacementlen && is_jmp(replacement[0])) { + /* direct jump */ recompute_jump(a, instr, replacement, insnbuf); + } if (a->instrlen > a->replacementlen) { add_nops(insnbuf + a->replacementlen,
Add alternative patching support for replacing an instruction with an indirect call. This will be needed for the paravirt alternatives. Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com> --- arch/x86/kernel/alternative.c | 22 +++++++++++++++------- 1 file changed, 15 insertions(+), 7 deletions(-)