| Message ID | CAMe9rOoXP7fz+XaM5hFnzDa=qSzz=8r3HkoddaTscrh7HUt03g@mail.gmail.com |
|---|---|
| State | New |
| Headers | show |
| Series | V2 [PATCH] Check multiple NT_GNU_PROPERTY_TYPE_0 notes [BZ #23509] | expand |
* H. J. Lu: > From e1c6cdeb7530c37ddb6688b17435c1c9a373a09c Mon Sep 17 00:00:00 2001 > From: "H.J. Lu" <hjl.tools@gmail.com> > Date: Fri, 10 Aug 2018 18:43:22 -0700 > Subject: [PATCH] Check multiple NT_GNU_PROPERTY_TYPE_0 notes [BZ #23509] > > The older linker treats .note.gnu.property section as a generic note > section and just concatenates all .note.gnu.property sections from the > inputs to the output. When the older linker is used to created the > program on CET-enabled OS, the generated output has .note.gnu.property > section with multiple NT_GNU_PROPERTY_TYPE_0 notes whose IBT and SHSTK > enable bits are set even if the program isn't CET enabled. Such program > will crash on CET-enabled machines. This patch updates the note parser: > > 1. Skip note parsing if a NT_GNU_PROPERTY_TYPE_0 note has been processed. > 2. Check multiple NT_GNU_PROPERTY_TYPE_0 notes. > > [BZ #23509] > * sysdeps/x86/dl-prop.h (_dl_process_cet_property_note): Skip > note parsing if a NT_GNU_PROPERTY_TYPE_0 note has been processed. > Update the l_cet field when processing NT_GNU_PROPERTY_TYPE_0 note. > Check multiple NT_GNU_PROPERTY_TYPE_0 notes. > * sysdeps/x86/link_map.h (l_cet): Expand to 3 bits, Add > lc_unknown. As far as I can tell, this patch catches only the case where a single PT_NOTE segment contains multiple notes. If there are multiple PT_NOTE segments with notes, and each one contains a single note, the patch will still enable CET. Is my summary accurate? Do you think it is safe to treat PT_NOTE segments in isolation? If yes, this should be mentioned in the commit message. This seems to be an unrelated change? + /* Property type must be in ascending order. */ + if (type < last_type) + return; Thanks, Florian
On Thu, Sep 20, 2018 at 1:54 AM, Florian Weimer <fweimer@redhat.com> wrote: > * H. J. Lu: > >> From e1c6cdeb7530c37ddb6688b17435c1c9a373a09c Mon Sep 17 00:00:00 2001 >> From: "H.J. Lu" <hjl.tools@gmail.com> >> Date: Fri, 10 Aug 2018 18:43:22 -0700 >> Subject: [PATCH] Check multiple NT_GNU_PROPERTY_TYPE_0 notes [BZ #23509] >> >> The older linker treats .note.gnu.property section as a generic note >> section and just concatenates all .note.gnu.property sections from the >> inputs to the output. When the older linker is used to created the >> program on CET-enabled OS, the generated output has .note.gnu.property >> section with multiple NT_GNU_PROPERTY_TYPE_0 notes whose IBT and SHSTK >> enable bits are set even if the program isn't CET enabled. Such program >> will crash on CET-enabled machines. This patch updates the note parser: >> >> 1. Skip note parsing if a NT_GNU_PROPERTY_TYPE_0 note has been processed. >> 2. Check multiple NT_GNU_PROPERTY_TYPE_0 notes. >> >> [BZ #23509] >> * sysdeps/x86/dl-prop.h (_dl_process_cet_property_note): Skip >> note parsing if a NT_GNU_PROPERTY_TYPE_0 note has been processed. >> Update the l_cet field when processing NT_GNU_PROPERTY_TYPE_0 note. >> Check multiple NT_GNU_PROPERTY_TYPE_0 notes. >> * sysdeps/x86/link_map.h (l_cet): Expand to 3 bits, Add >> lc_unknown. > > As far as I can tell, this patch catches only the case where a single > PT_NOTE segment contains multiple notes. If there are multiple PT_NOTE > segments with notes, and each one contains a single note, the patch will > still enable CET. I believe this is covered by CET smoke test: https://github.com/hjl-tools/cet-smoke-test My patch should work in all cases. If it misses some cases, please add it to master branch at https://github.com/hjl-tools/cet-smoke-test under the "note" directory. > Is my summary accurate? Do you think it is safe to treat PT_NOTE > segments in isolation? What do you mean by that? The only assumption I made is that property note must follow the spec. Any violation makes it invalid. > If yes, this should be mentioned in the commit message. > > This seems to be an unrelated change? > > + /* Property type must be in ascending order. */ > + if (type < last_type) > + return; > This is the part of property spec. If properties aren't properly sorted, it is invalid.
* H. J. Lu: >> As far as I can tell, this patch catches only the case where a single >> PT_NOTE segment contains multiple notes. If there are multiple PT_NOTE >> segments with notes, and each one contains a single note, the patch will >> still enable CET. > > I believe this is covered by CET smoke test: > > https://github.com/hjl-tools/cet-smoke-test > > My patch should work in all cases. If it misses some cases, please add it > to master branch at > > https://github.com/hjl-tools/cet-smoke-test > > under the "note" directory. > >> Is my summary accurate? Do you think it is safe to treat PT_NOTE >> segments in isolation? > > What do you mean by that? The only assumption I made is that > property note must follow the spec. Any violation makes it invalid. I'm attaching a patched executable which has two PT_NOTE segments with separately valid GNU property notes (if I did my patching correctly). I think your code will still accept it. It is conceivable that a linker which is not aware of the required merging for property notes would create such segments, I think. >> If yes, this should be mentioned in the commit message. >> >> This seems to be an unrelated change? >> >> + /* Property type must be in ascending order. */ >> + if (type < last_type) >> + return; >> > > This is the part of property spec. If properties aren't properly > sorted, it is invalid. Okay, that part makes sense because it's internal to the notes AFAICS. And note merging without GNU property note awareness will likely violate this constraint. Maybe you could add a comment to this effect? Thanks, Florian
On Fri, Sep 21, 2018 at 7:49 AM, Florian Weimer <fweimer@redhat.com> wrote: > * H. J. Lu: > >>> As far as I can tell, this patch catches only the case where a single >>> PT_NOTE segment contains multiple notes. If there are multiple PT_NOTE >>> segments with notes, and each one contains a single note, the patch will >>> still enable CET. >> >> I believe this is covered by CET smoke test: >> >> https://github.com/hjl-tools/cet-smoke-test >> >> My patch should work in all cases. If it misses some cases, please add it >> to master branch at >> >> https://github.com/hjl-tools/cet-smoke-test >> >> under the "note" directory. >> >>> Is my summary accurate? Do you think it is safe to treat PT_NOTE >>> segments in isolation? >> >> What do you mean by that? The only assumption I made is that >> property note must follow the spec. Any violation makes it invalid. > > I'm attaching a patched executable which has two PT_NOTE segments with > separately valid GNU property notes (if I did my patching correctly). > > I think your code will still accept it. It is conceivable that a linker > which is not aware of the required merging for property notes would > create such segments, I think. My goal is to allow older linkers which don't understand property notes to generate working executables on CET enabled OS. It isn't tended to handle all hand-crafted binaries. The worst case is that such binaries won't run on CET enabled OS. I don't believe it is an issue. It may even be a bonus. Do you have a testcase which may be generated by an old linker on CET enabled OS? >>> If yes, this should be mentioned in the commit message. >>> >>> This seems to be an unrelated change? >>> >>> + /* Property type must be in ascending order. */ >>> + if (type < last_type) >>> + return; >>> >> >> This is the part of property spec. If properties aren't properly >> sorted, it is invalid. > > Okay, that part makes sense because it's internal to the notes AFAICS. > And note merging without GNU property note awareness will likely violate > this constraint. Maybe you could add a comment to this effect? I updated comments to /* Property types must be sorted in ascending order. Ignore property note with the wrong type order. */ if (type < last_type) return; Thanks.
* H. J. Lu: > My goal is to allow older linkers which don't understand property notes > to generate working executables on CET enabled OS. It isn't tended to > handle all hand-crafted binaries. The worst case is that such binaries > won't run on CET enabled OS. I don't believe it is an issue. It may even > be a bonus. > > Do you have a testcase which may be generated by an old linker on > CET enabled OS? My position is that ELF is an open format and that we don't really know what kind of link editors are out there and are used in practice. Other views are certainly possible. I mainly wanted to understand the rationale behind the code. If you do not expect multiple PT_NOTE segments with properly aligned property notes, I think that's okay. We can adjust the dynamic linker again if such binaries show up in the future. >> Okay, that part makes sense because it's internal to the notes AFAICS. >> And note merging without GNU property note awareness will likely violate >> this constraint. Maybe you could add a comment to this effect? > > I updated comments to > > /* Property types must be sorted in ascending order. > Ignore property note with the wrong type order. */ > if (type < last_type) > return; Thanks. Florian
* Florian Weimer: >>> If yes, this should be mentioned in the commit message. >>> >>> This seems to be an unrelated change? >>> >>> + /* Property type must be in ascending order. */ >>> + if (type < last_type) >>> + return; >>> >> >> This is the part of property spec. If properties aren't properly >> sorted, it is invalid. > > Okay, that part makes sense because it's internal to the notes AFAICS. > And note merging without GNU property note awareness will likely violate > this constraint. Maybe you could add a comment to this effect? Hmm, isn't the point that this is the internal type in the note (not the tag), and there isn't any *note* merging, only note *section* merging in an old linker. The latter leaves the note boundaries intact, so the internal layout will be unmodified. Or am I confused about this? Thanks, Florian
* H. J. Lu: > The older linker treats .note.gnu.property section as a generic note > section and just concatenates all .note.gnu.property sections from the > inputs to the output. When the older linker is used to created the > program on CET-enabled OS, the generated output has .note.gnu.property > section with multiple NT_GNU_PROPERTY_TYPE_0 notes whose IBT and SHSTK > enable bits are set even if the program isn't CET enabled. Such program > will crash on CET-enabled machines. This patch updates the note parser: > > 1. Skip note parsing if a NT_GNU_PROPERTY_TYPE_0 note has been processed. > 2. Check multiple NT_GNU_PROPERTY_TYPE_0 notes. > > [BZ #23509] > * sysdeps/x86/dl-prop.h (_dl_process_cet_property_note): Skip > note parsing if a NT_GNU_PROPERTY_TYPE_0 note has been processed. > Update the l_cet field when processing NT_GNU_PROPERTY_TYPE_0 note. > Check multiple NT_GNU_PROPERTY_TYPE_0 notes. > * sysdeps/x86/link_map.h (l_cet): Expand to 3 bits, Add > lc_unknown. I would like to move this forward. I think the code is okay, as long as we are confident that older linkers will not produce multiple PT_NOTE segments, each containing one NT_GNU_PROPERTY_TYPE_0 note. Maybe this should be mentioned in the commit message (assuming that you agree that my understanding of the code is correct). Thanks, Florian
On Wed, Nov 7, 2018 at 10:27 AM Florian Weimer <fweimer@redhat.com> wrote: > > * Florian Weimer: > > >>> If yes, this should be mentioned in the commit message. > >>> > >>> This seems to be an unrelated change? > >>> > >>> + /* Property type must be in ascending order. */ > >>> + if (type < last_type) > >>> + return; > >>> > >> > >> This is the part of property spec. If properties aren't properly > >> sorted, it is invalid. > > > > Okay, that part makes sense because it's internal to the notes AFAICS. > > And note merging without GNU property note awareness will likely violate > > this constraint. Maybe you could add a comment to this effect? > > Hmm, isn't the point that this is the internal type in the note (not the > tag), and there isn't any *note* merging, only note *section* merging in > an old linker. The latter leaves the note boundaries intact, so the > internal layout will be unmodified. > Older linkers will concatenate all input GNU property note sections into a single output GNU property note section without merging them.
On Wed, Nov 7, 2018 at 10:32 AM Florian Weimer <fweimer@redhat.com> wrote: > > * H. J. Lu: > > > The older linker treats .note.gnu.property section as a generic note > > section and just concatenates all .note.gnu.property sections from the > > inputs to the output. When the older linker is used to created the > > program on CET-enabled OS, the generated output has .note.gnu.property > > section with multiple NT_GNU_PROPERTY_TYPE_0 notes whose IBT and SHSTK > > enable bits are set even if the program isn't CET enabled. Such program > > will crash on CET-enabled machines. This patch updates the note parser: > > > > 1. Skip note parsing if a NT_GNU_PROPERTY_TYPE_0 note has been processed. > > 2. Check multiple NT_GNU_PROPERTY_TYPE_0 notes. > > > > [BZ #23509] > > * sysdeps/x86/dl-prop.h (_dl_process_cet_property_note): Skip > > note parsing if a NT_GNU_PROPERTY_TYPE_0 note has been processed. > > Update the l_cet field when processing NT_GNU_PROPERTY_TYPE_0 note. > > Check multiple NT_GNU_PROPERTY_TYPE_0 notes. > > * sysdeps/x86/link_map.h (l_cet): Expand to 3 bits, Add > > lc_unknown. > > I would like to move this forward. > > I think the code is okay, as long as we are confident that older linkers > will not produce multiple PT_NOTE segments, each containing one > NT_GNU_PROPERTY_TYPE_0 note. Maybe this should be mentioned in the > commit message (assuming that you agree that my understanding of the > code is correct). > Like this?
* H. J. Lu: > On Wed, Nov 7, 2018 at 10:32 AM Florian Weimer <fweimer@redhat.com> wrote: >> >> * H. J. Lu: >> >> > The older linker treats .note.gnu.property section as a generic note >> > section and just concatenates all .note.gnu.property sections from the >> > inputs to the output. When the older linker is used to created the >> > program on CET-enabled OS, the generated output has .note.gnu.property >> > section with multiple NT_GNU_PROPERTY_TYPE_0 notes whose IBT and SHSTK >> > enable bits are set even if the program isn't CET enabled. Such program >> > will crash on CET-enabled machines. This patch updates the note parser: >> > >> > 1. Skip note parsing if a NT_GNU_PROPERTY_TYPE_0 note has been processed. >> > 2. Check multiple NT_GNU_PROPERTY_TYPE_0 notes. >> > >> > [BZ #23509] >> > * sysdeps/x86/dl-prop.h (_dl_process_cet_property_note): Skip >> > note parsing if a NT_GNU_PROPERTY_TYPE_0 note has been processed. >> > Update the l_cet field when processing NT_GNU_PROPERTY_TYPE_0 note. >> > Check multiple NT_GNU_PROPERTY_TYPE_0 notes. >> > * sysdeps/x86/link_map.h (l_cet): Expand to 3 bits, Add >> > lc_unknown. >> >> I would like to move this forward. >> >> I think the code is okay, as long as we are confident that older linkers >> will not produce multiple PT_NOTE segments, each containing one >> NT_GNU_PROPERTY_TYPE_0 note. Maybe this should be mentioned in the >> commit message (assuming that you agree that my understanding of the >> code is correct). >> > > Like this? Sorry, let me rephrase: The commit message talks about sections, not segments. The code deals with PT_NOTE segments, obviously. Old linkers produce multiple PT_NOTE segments for the *same* alignment if they process multiple note sections with differing alignment in a certain order. (It does not happen always.) Based on reading the code, I think that if the first PT_NOTE segment it encounters contains one NT_GNU_PROPERTY_TYPE_0 note that enables CET, it will enable CET even if the loader produced multiple PT_NOTE segments, and there is another (unmerged) NT_GNU_PROPERTY_TYPE_0 note in a subsequent PT_NOTE segment. This means that the current code can still incorrectly enable CET in cases where an old linker produced a multitude of PT_NOTE sections. Based on the patch and the discussion so far it is unclear to me whether you have analyzed the issue and concluded that split PT_NOTE segments of the same alignment (as generated by old linkers in some cases) are not relevant, or if it is an accidental omission in the patch. The explaination in the patch itself does not help because of the section/segment discrepancy I mentioned first. Thanks, Florian
On Thu, Nov 8, 2018 at 2:52 AM Florian Weimer <fweimer@redhat.com> wrote: > > * H. J. Lu: > > > On Wed, Nov 7, 2018 at 10:32 AM Florian Weimer <fweimer@redhat.com> wrote: > >> > >> * H. J. Lu: > >> > >> > The older linker treats .note.gnu.property section as a generic note > >> > section and just concatenates all .note.gnu.property sections from the > >> > inputs to the output. When the older linker is used to created the > >> > program on CET-enabled OS, the generated output has .note.gnu.property > >> > section with multiple NT_GNU_PROPERTY_TYPE_0 notes whose IBT and SHSTK > >> > enable bits are set even if the program isn't CET enabled. Such program > >> > will crash on CET-enabled machines. This patch updates the note parser: > >> > > >> > 1. Skip note parsing if a NT_GNU_PROPERTY_TYPE_0 note has been processed. > >> > 2. Check multiple NT_GNU_PROPERTY_TYPE_0 notes. > >> > > >> > [BZ #23509] > >> > * sysdeps/x86/dl-prop.h (_dl_process_cet_property_note): Skip > >> > note parsing if a NT_GNU_PROPERTY_TYPE_0 note has been processed. > >> > Update the l_cet field when processing NT_GNU_PROPERTY_TYPE_0 note. > >> > Check multiple NT_GNU_PROPERTY_TYPE_0 notes. > >> > * sysdeps/x86/link_map.h (l_cet): Expand to 3 bits, Add > >> > lc_unknown. > >> > >> I would like to move this forward. > >> > >> I think the code is okay, as long as we are confident that older linkers > >> will not produce multiple PT_NOTE segments, each containing one > >> NT_GNU_PROPERTY_TYPE_0 note. Maybe this should be mentioned in the > >> commit message (assuming that you agree that my understanding of the > >> code is correct). > >> > > > > Like this? > > Sorry, let me rephrase: > > The commit message talks about sections, not segments. The code deals > with PT_NOTE segments, obviously. See my reply before. > Old linkers produce multiple PT_NOTE segments for the *same* alignment > if they process multiple note sections with differing alignment in a > certain order. (It does not happen always.) True. > Based on reading the code, I think that if the first PT_NOTE segment it > encounters contains one NT_GNU_PROPERTY_TYPE_0 note that enables CET, it > will enable CET even if the loader produced multiple PT_NOTE segments, > and there is another (unmerged) NT_GNU_PROPERTY_TYPE_0 note in a > subsequent PT_NOTE segment. This means that the current code can still > incorrectly enable CET in cases where an old linker produced a multitude > of PT_NOTE sections. Linkers group input note sections with the same name into a single output note section with the same name. One output note section is placed in one PT_NOTE segment. There won't be "another (unmerged) NT_GNU_PROPERTY_TYPE_0 note in a subsequent PT_NOTE segment." > Based on the patch and the discussion so far it is unclear to me whether > you have analyzed the issue and concluded that split PT_NOTE segments of > the same alignment (as generated by old linkers in some cases) are not > relevant, or if it is an accidental omission in the patch. The > explaination in the patch itself does not help because of the > section/segment discrepancy I mentioned first. >
On Thu, Nov 8, 2018 at 5:15 AM H.J. Lu <hjl.tools@gmail.com> wrote: > > On Thu, Nov 8, 2018 at 2:52 AM Florian Weimer <fweimer@redhat.com> wrote: > > > > * H. J. Lu: > > > > > On Wed, Nov 7, 2018 at 10:32 AM Florian Weimer <fweimer@redhat.com> wrote: > > >> > > >> * H. J. Lu: > > >> > > >> > The older linker treats .note.gnu.property section as a generic note > > >> > section and just concatenates all .note.gnu.property sections from the > > >> > inputs to the output. When the older linker is used to created the > > >> > program on CET-enabled OS, the generated output has .note.gnu.property > > >> > section with multiple NT_GNU_PROPERTY_TYPE_0 notes whose IBT and SHSTK > > >> > enable bits are set even if the program isn't CET enabled. Such program > > >> > will crash on CET-enabled machines. This patch updates the note parser: > > >> > > > >> > 1. Skip note parsing if a NT_GNU_PROPERTY_TYPE_0 note has been processed. > > >> > 2. Check multiple NT_GNU_PROPERTY_TYPE_0 notes. > > >> > > > >> > [BZ #23509] > > >> > * sysdeps/x86/dl-prop.h (_dl_process_cet_property_note): Skip > > >> > note parsing if a NT_GNU_PROPERTY_TYPE_0 note has been processed. > > >> > Update the l_cet field when processing NT_GNU_PROPERTY_TYPE_0 note. > > >> > Check multiple NT_GNU_PROPERTY_TYPE_0 notes. > > >> > * sysdeps/x86/link_map.h (l_cet): Expand to 3 bits, Add > > >> > lc_unknown. > > >> > > >> I would like to move this forward. > > >> > > >> I think the code is okay, as long as we are confident that older linkers > > >> will not produce multiple PT_NOTE segments, each containing one > > >> NT_GNU_PROPERTY_TYPE_0 note. Maybe this should be mentioned in the > > >> commit message (assuming that you agree that my understanding of the > > >> code is correct). > > >> > > > > > > Like this? > > > > Sorry, let me rephrase: > > > > The commit message talks about sections, not segments. The code deals > > with PT_NOTE segments, obviously. > > See my reply before. > > > Old linkers produce multiple PT_NOTE segments for the *same* alignment > > if they process multiple note sections with differing alignment in a > > certain order. (It does not happen always.) > > True. > > > Based on reading the code, I think that if the first PT_NOTE segment it > > encounters contains one NT_GNU_PROPERTY_TYPE_0 note that enables CET, it > > will enable CET even if the loader produced multiple PT_NOTE segments, > > and there is another (unmerged) NT_GNU_PROPERTY_TYPE_0 note in a > > subsequent PT_NOTE segment. This means that the current code can still > > incorrectly enable CET in cases where an old linker produced a multitude > > of PT_NOTE sections. > > Linkers group input note sections with the same name into a single output note > section with the same name. One output note section is placed in one PT_NOTE > segment. There won't be "another (unmerged) NT_GNU_PROPERTY_TYPE_0 > note in a subsequent PT_NOTE segment." > > > Based on the patch and the discussion so far it is unclear to me whether > > you have analyzed the issue and concluded that split PT_NOTE segments of > > the same alignment (as generated by old linkers in some cases) are not > > relevant, or if it is an accidental omission in the patch. The > > explaination in the patch itself does not help because of the > > section/segment discrepancy I mentioned first. > > Here is the updated patch with Linkers group input note sections with the same name into one output note section with the same name. One output note section is placed in one PT_NOTE segment. Since new linkers merge input .note.gnu.property sections into one output .note.gnu.property section, there is only one NT_GNU_PROPERTY_TYPE_0 note in one PT_NOTE segment with new linkers. Since older linkers treat input .note.gnu.property section as a generic note section and just concatenate all input .note.gnu.property sections into one output .note.gnu.property section without merging them, we may see multiple NT_GNU_PROPERTY_TYPE_0 notes in one PT_NOTE segment with older linkers.
* H. J. Lu: > Here is the updated patch with > > Linkers group input note sections with the same name into one output > note section with the same name. One output note section is placed in > one PT_NOTE segment. Since new linkers merge input .note.gnu.property > sections into one output .note.gnu.property section, there is only > one NT_GNU_PROPERTY_TYPE_0 note in one PT_NOTE segment with new linkers. > Since older linkers treat input .note.gnu.property section as a generic > note section and just concatenate all input .note.gnu.property sections > into one output .note.gnu.property section without merging them, we may > see multiple NT_GNU_PROPERTY_TYPE_0 notes in one PT_NOTE segment with > older linkers. Thanks. This hypothesis regarding older linkers seems reasonable, and the explanation is very clear now. The code looks okay to me. Would you please backport this to the 2.28 release branch as well? Thanks, Florian
On Thu, Nov 8, 2018 at 9:41 AM Florian Weimer <fweimer@redhat.com> wrote: > > * H. J. Lu: > > > Here is the updated patch with > > > > Linkers group input note sections with the same name into one output > > note section with the same name. One output note section is placed in > > one PT_NOTE segment. Since new linkers merge input .note.gnu.property > > sections into one output .note.gnu.property section, there is only > > one NT_GNU_PROPERTY_TYPE_0 note in one PT_NOTE segment with new linkers. > > Since older linkers treat input .note.gnu.property section as a generic > > note section and just concatenate all input .note.gnu.property sections > > into one output .note.gnu.property section without merging them, we may > > see multiple NT_GNU_PROPERTY_TYPE_0 notes in one PT_NOTE segment with > > older linkers. > > Thanks. This hypothesis regarding older linkers seems reasonable, and > the explanation is very clear now. The code looks okay to me. I checked it into master branch. > Would you please backport this to the 2.28 release branch as well? > I am backporting this patch to 2.28 branch.
From e1c6cdeb7530c37ddb6688b17435c1c9a373a09c Mon Sep 17 00:00:00 2001 From: "H.J. Lu" <hjl.tools@gmail.com> Date: Fri, 10 Aug 2018 18:43:22 -0700 Subject: [PATCH] Check multiple NT_GNU_PROPERTY_TYPE_0 notes [BZ #23509] The older linker treats .note.gnu.property section as a generic note section and just concatenates all .note.gnu.property sections from the inputs to the output. When the older linker is used to created the program on CET-enabled OS, the generated output has .note.gnu.property section with multiple NT_GNU_PROPERTY_TYPE_0 notes whose IBT and SHSTK enable bits are set even if the program isn't CET enabled. Such program will crash on CET-enabled machines. This patch updates the note parser: 1. Skip note parsing if a NT_GNU_PROPERTY_TYPE_0 note has been processed. 2. Check multiple NT_GNU_PROPERTY_TYPE_0 notes. [BZ #23509] * sysdeps/x86/dl-prop.h (_dl_process_cet_property_note): Skip note parsing if a NT_GNU_PROPERTY_TYPE_0 note has been processed. Update the l_cet field when processing NT_GNU_PROPERTY_TYPE_0 note. Check multiple NT_GNU_PROPERTY_TYPE_0 notes. * sysdeps/x86/link_map.h (l_cet): Expand to 3 bits, Add lc_unknown. --- sysdeps/x86/dl-prop.h | 51 +++++++++++++++++++++++++++++++++--------- sysdeps/x86/link_map.h | 9 ++++---- 2 files changed, 46 insertions(+), 14 deletions(-) diff --git a/sysdeps/x86/dl-prop.h b/sysdeps/x86/dl-prop.h index 26c3131ac5..9ab890d12b 100644 --- a/sysdeps/x86/dl-prop.h +++ b/sysdeps/x86/dl-prop.h @@ -49,6 +49,10 @@ _dl_process_cet_property_note (struct link_map *l, const ElfW(Addr) align) { #if CET_ENABLED + /* Skip if we have seen a NT_GNU_PROPERTY_TYPE_0 note before. */ + if (l->l_cet != lc_unknown) + return; + /* The NT_GNU_PROPERTY_TYPE_0 note must be aliged to 4 bytes in 32-bit objects and to 8 bytes in 64-bit objects. Skip notes with incorrect alignment. */ @@ -57,6 +61,9 @@ _dl_process_cet_property_note (struct link_map *l, const ElfW(Addr) start = (ElfW(Addr)) note; + unsigned int feature_1 = 0; + unsigned int last_type = 0; + while ((ElfW(Addr)) (note + 1) - start < size) { /* Find the NT_GNU_PROPERTY_TYPE_0 note. */ @@ -64,10 +71,18 @@ _dl_process_cet_property_note (struct link_map *l, && note->n_type == NT_GNU_PROPERTY_TYPE_0 && memcmp (note + 1, "GNU", 4) == 0) { + /* Stop if we see more than one GNU property note which may + be generated by the older linker. */ + if (l->l_cet != lc_unknown) + return; + + /* Check CET status now. */ + l->l_cet = lc_none; + /* Check for invalid property. */ if (note->n_descsz < 8 || (note->n_descsz % sizeof (ElfW(Addr))) != 0) - break; + return; /* Start and end of property array. */ unsigned char *ptr = (unsigned char *) (note + 1) + 4; @@ -78,9 +93,15 @@ _dl_process_cet_property_note (struct link_map *l, unsigned int type = *(unsigned int *) ptr; unsigned int datasz = *(unsigned int *) (ptr + 4); + /* Property type must be in ascending order. */ + if (type < last_type) + return; + ptr += 8; if ((ptr + datasz) > ptr_end) - break; + return; + + last_type = type; if (type == GNU_PROPERTY_X86_FEATURE_1_AND) { @@ -89,14 +110,18 @@ _dl_process_cet_property_note (struct link_map *l, we stop the search regardless if its size is correct or not. There is no point to continue if this note is ill-formed. */ - if (datasz == 4) - { - unsigned int feature_1 = *(unsigned int *) ptr; - if ((feature_1 & GNU_PROPERTY_X86_FEATURE_1_IBT)) - l->l_cet |= lc_ibt; - if ((feature_1 & GNU_PROPERTY_X86_FEATURE_1_SHSTK)) - l->l_cet |= lc_shstk; - } + if (datasz != 4) + return; + + feature_1 = *(unsigned int *) ptr; + + /* Keep searching for the next GNU property note + generated by the older linker. */ + break; + } + else if (type > GNU_PROPERTY_X86_FEATURE_1_AND) + { + /* Stop since property type is in ascending order. */ return; } @@ -112,6 +137,12 @@ _dl_process_cet_property_note (struct link_map *l, + ELF_NOTE_NEXT_OFFSET (note->n_namesz, note->n_descsz, align)); } + + /* We get here only if there is one or no GNU property note. */ + if ((feature_1 & GNU_PROPERTY_X86_FEATURE_1_IBT)) + l->l_cet |= lc_ibt; + if ((feature_1 & GNU_PROPERTY_X86_FEATURE_1_SHSTK)) + l->l_cet |= lc_shstk; #endif } diff --git a/sysdeps/x86/link_map.h b/sysdeps/x86/link_map.h index ef1206a9d2..9367ed0889 100644 --- a/sysdeps/x86/link_map.h +++ b/sysdeps/x86/link_map.h @@ -19,8 +19,9 @@ /* If this object is enabled with CET. */ enum { - lc_none = 0, /* Not enabled with CET. */ - lc_ibt = 1 << 0, /* Enabled with IBT. */ - lc_shstk = 1 << 1, /* Enabled with STSHK. */ + lc_unknown = 0, /* Unknown CET status. */ + lc_none = 1 << 0, /* Not enabled with CET. */ + lc_ibt = 1 << 1, /* Enabled with IBT. */ + lc_shstk = 1 << 2, /* Enabled with STSHK. */ lc_ibt_and_shstk = lc_ibt | lc_shstk /* Enabled with both. */ - } l_cet:2; + } l_cet:3; -- 2.17.1