[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH v6 3/6] livepatch: NOP if func->new_addr is zero.
On Mon, Sep 19, 2016 at 10:31:23AM -0600, Jan Beulich wrote: > >>> On 19.09.16 at 18:11, <konrad.wilk@xxxxxxxxxx> wrote: > > On Mon, Sep 19, 2016 at 02:59:32AM -0600, Jan Beulich wrote: > >> >>> On 16.09.16 at 17:29, <konrad.wilk@xxxxxxxxxx> wrote: > >> > @@ -31,11 +30,11 @@ void arch_livepatch_revive(void) > >> > > >> > int arch_livepatch_verify_func(const struct livepatch_func *func) > >> > { > >> > - /* No NOP patching yet. */ > >> > - if ( !func->new_size ) > >> > + /* If NOPing only do up to maximum amount we can put in the > >> > ->opaque. */ > >> > + if ( !func->new_addr && func->new_size > sizeof(func->opaque) ) > >> > return -EOPNOTSUPP; > >> > > >> > - if ( func->old_size < PATCH_INSN_SIZE ) > >> > + if ( func->old_size < ARCH_PATCH_INSN_SIZE ) > >> > return -EINVAL; > >> > >> Is that indeed a requirement when NOPing? You can easily NOP out > >> just a single byte on x86. Or shouldn't in that case old_size == new_size > >> anyway? In which case the comment further down stating that new_size > > > > The original intent behind .old_size was to guard against patching > > functions that were less than our relative jump. > > > > (The tools end up computing the .old_size as the size of the whole function > > which is fine). > > > > But with this NOPing support, you are right - we could have now an > > function that is say 4 bytes long and we only need to NOP three bytes > > out of it (the last instruction I assume would be 'ret'). > > > > So perhaps this check needs just needs an 'else if' , like so: > > > > int arch_livepatch_verify_func(const struct livepatch_func *func) > > { > > /* If NOPing.. */ > > if ( !func->new_addr ) > > { > > /* Only do up to maximum amount we can put in the ->opaque. */ > > if ( func->new_size > sizeof(func->opaque) ) > > return -EOPNOTSUPP; > > > > /* One instruction for 'ret' and the other to NOP. */ > > if ( func->old_size < 2 ) > > return -EINVAL; > > } > > else if ( func->old_size < ARCH_PATCH_INSN_SIZE ) > > return -EINVAL; > > > > return 0; > > } > > Except that I wouldn't use 2, to not exclude patching out some > single byte in the middle of a function, without regard to what the > function's actual size is. Uh-uh. The _new_size_ determines how many bytes to NOP (in the context of this patch). The old_size (where we check to be at min 2) is a safety valve to make sure we don't NOP something outside the function. ..snip.. > >> NOP addition here, perhaps worth dropping the _jmp from the > >> function name (and its revert counterpart)? > > > > Ooh, good idea. But I think it maybe better as a seperate patch (as it > > also touches the ARM code). > > That's in the other series, isn't it? It expands the existing ones. Right now in 'staging' branch we have an arch/arm/livepatch.c which has these functions in it. Granted nothing compiles them, so I could break it in this patch. But I already cobbled up the patch so may as well use it? From 45abdd6a0c3a6a2ca7180c7340032ac5b2b186a4 Mon Sep 17 00:00:00 2001 From: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx> Date: Mon, 19 Sep 2016 12:20:27 -0400 Subject: [PATCH] livepatch: Drop _jmp from arch_livepatch_[apply,revert]_jmp With "livepatch: NOP if func->new_addr is zero." that name makes no more sense. Suggested-by: Jan Beulich <jbeulich@xxxxxxxx> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx> --- v7: New submission --- xen/arch/arm/livepatch.c | 4 ++-- xen/arch/x86/livepatch.c | 4 ++-- xen/include/xen/livepatch.h | 4 ++-- 3 files changed, 6 insertions(+), 6 deletions(-) diff --git a/xen/arch/arm/livepatch.c b/xen/arch/arm/livepatch.c index 755f596..7f067a0 100644 --- a/xen/arch/arm/livepatch.c +++ b/xen/arch/arm/livepatch.c @@ -21,11 +21,11 @@ int arch_livepatch_verify_func(const struct livepatch_func *func) return -ENOSYS; } -void arch_livepatch_apply_jmp(struct livepatch_func *func) +void arch_livepatch_apply(struct livepatch_func *func) { } -void arch_livepatch_revert_jmp(const struct livepatch_func *func) +void arch_livepatch_revert(const struct livepatch_func *func) { } diff --git a/xen/arch/x86/livepatch.c b/xen/arch/x86/livepatch.c index 118770e..36bbc5f 100644 --- a/xen/arch/x86/livepatch.c +++ b/xen/arch/x86/livepatch.c @@ -47,7 +47,7 @@ int arch_livepatch_verify_func(const struct livepatch_func *func) return 0; } -void arch_livepatch_apply_jmp(struct livepatch_func *func) +void arch_livepatch_apply(struct livepatch_func *func) { uint8_t *old_ptr; uint8_t insn[sizeof(func->opaque)]; @@ -76,7 +76,7 @@ void arch_livepatch_apply_jmp(struct livepatch_func *func) memcpy(old_ptr, insn, len); } -void arch_livepatch_revert_jmp(const struct livepatch_func *func) +void arch_livepatch_revert(const struct livepatch_func *func) { memcpy(func->old_addr, func->opaque, livepatch_insn_len(func)); } diff --git a/xen/include/xen/livepatch.h b/xen/include/xen/livepatch.h index 174af06..b7f66d4 100644 --- a/xen/include/xen/livepatch.h +++ b/xen/include/xen/livepatch.h @@ -86,8 +86,8 @@ unsigned int livepatch_insn_len(const struct livepatch_func *func) int arch_livepatch_quiesce(void); void arch_livepatch_revive(void); -void arch_livepatch_apply_jmp(struct livepatch_func *func); -void arch_livepatch_revert_jmp(const struct livepatch_func *func); +void arch_livepatch_apply(struct livepatch_func *func); +void arch_livepatch_revert(const struct livepatch_func *func); void arch_livepatch_post_action(void); void arch_livepatch_mask(void); -- 2.4.11 > > Jan > _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx https://lists.xen.org/xen-devel
|
Lists.xenproject.org is hosted with RackSpace, monitoring our |