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Message-ID: <87r1pabu9g.fsf@oldenburg2.str.redhat.com>
Date: Tue, 03 Nov 2020 11:38:03 +0100
From: Florian Weimer <fweimer@...hat.com>
To: Szabolcs Nagy <szabolcs.nagy@....com>
Cc: libc-alpha@...rceware.org, Jeremy Linton <jeremy.linton@....com>,
Catalin Marinas <catalin.marinas@....com>,
Mark Rutland <mark.rutland@....com>,
Will Deacon <will.deacon@....com>, Mark Brown <broonie@...nel.org>,
Kees Cook <keescook@...omium.org>,
Salvatore Mesoraca <s.mesoraca16@...il.com>,
Lennart Poettering <mzxreary@...inter.de>,
Topi Miettinen <toiwoton@...il.com>, linux-kernel@...r.kernel.org,
linux-arm-kernel@...ts.infradead.org,
kernel-hardening@...ts.openwall.com, linux-hardening@...r.kernel.org,
"H.J. Lu" <hjl.tools@...il.com>
Subject: Re: [PATCH 2/4] elf: Move note processing after l_phdr is updated
[BZ #26831]
* Szabolcs Nagy:
> Program headers are processed in two pass: after the first pass
> load segments are mmapped so in the second pass target specific
> note processing logic can access the notes.
>
> The second pass is moved later so various link_map fields are
> set up that may be useful for note processing such as l_phdr.
> ---
> elf/dl-load.c | 30 +++++++++++++++---------------
> 1 file changed, 15 insertions(+), 15 deletions(-)
>
> diff --git a/elf/dl-load.c b/elf/dl-load.c
> index ceaab7f18e..673cf960a0 100644
> --- a/elf/dl-load.c
> +++ b/elf/dl-load.c
> @@ -1259,21 +1259,6 @@ _dl_map_object_from_fd (const char *name, const char *origname, int fd,
> maplength, has_holes, loader);
> if (__glibc_unlikely (errstring != NULL))
> goto call_lose;
> -
> - /* Process program headers again after load segments are mapped in
> - case processing requires accessing those segments. Scan program
> - headers backward so that PT_NOTE can be skipped if PT_GNU_PROPERTY
> - exits. */
> - for (ph = &phdr[l->l_phnum]; ph != phdr; --ph)
> - switch (ph[-1].p_type)
> - {
> - case PT_NOTE:
> - _dl_process_pt_note (l, fd, &ph[-1]);
> - break;
> - case PT_GNU_PROPERTY:
> - _dl_process_pt_gnu_property (l, fd, &ph[-1]);
> - break;
> - }
> }
>
> if (l->l_ld == 0)
> @@ -1481,6 +1466,21 @@ cannot enable executable stack as shared object requires");
> /* Assign the next available module ID. */
> l->l_tls_modid = _dl_next_tls_modid ();
>
> + /* Process program headers again after load segments are mapped in
> + case processing requires accessing those segments. Scan program
> + headers backward so that PT_NOTE can be skipped if PT_GNU_PROPERTY
> + exits. */
> + for (ph = &l->l_phdr[l->l_phnum]; ph != l->l_phdr; --ph)
> + switch (ph[-1].p_type)
> + {
> + case PT_NOTE:
> + _dl_process_pt_note (l, fd, &ph[-1]);
> + break;
> + case PT_GNU_PROPERTY:
> + _dl_process_pt_gnu_property (l, fd, &ph[-1]);
> + break;
> + }
> +
> #ifdef DL_AFTER_LOAD
> DL_AFTER_LOAD (l);
> #endif
Is this still compatible with the CET requirements?
I hope it is because the CET magic happens in _dl_open_check, so after
the the code in elf/dl-load.c has run.
Thanks,
Florian
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