on several targets the rtld entry point (_dl_start_user) adjusts argv on the stack to have it right for the executed application and to avoid a misaligned sp in the application elf entry point. getauxval seems to use a global GLRO(dl_auxv) value that is computed before the adjustments. affects at least aarch64 and arm. $ cat a.c #include <stdio.h> #include <sys/auxv.h> int main() { for (int i=0; i < 40; i++) printf("%2d 0x%lx\n", i, getauxval(i)); } $ ./a.out 0 0x0 1 0x0 2 0x0 3 0xaaaad59e5040 4 0x38 5 0x8 6 0x1000 7 0xffff9c5fd000 8 0x0 9 0xaaaad59e5670 10 0x0 11 0x3e8 12 0x3e8 13 0x3e8 14 0x3e8 15 0xffffce3884b8 16 0x807 17 0x64 18 0x0 19 0x0 20 0x0 21 0x0 22 0x0 23 0x0 24 0x0 25 0xffffce3884a8 26 0x0 27 0x0 28 0x0 29 0x0 30 0x0 31 0xffffce388ff0 32 0x0 33 0xffff9c628000 34 0x0 35 0x0 36 0x0 37 0x0 38 0x0 39 0x0 $ /lib/ld-linux-aarch64.so.1 ./a.out 0 0x0 1 0x0 2 0x0 3 0x0 4 0x0 5 0x0 6 0x0 7 0x0 8 0x7 9 0x0 10 0x0 11 0x0 12 0x0 13 0x0 14 0x0 15 0x0 16 0x807 17 0x0 18 0x0 19 0x0 20 0x0 21 0x0 22 0x0 23 0x0 24 0x0 25 0x0 26 0x0 27 0x0 28 0x0 29 0x0 30 0x0 31 0x0 32 0x0 33 0x0 34 0x0 35 0x0 36 0x0 37 0x0 38 0x0 39 0x0
i think it affects all targets with DL_ARGV_NOT_RELRO == 1
I've just run into this because it causes a glibc test failure when libnss-systemd is enabled (https://bugs.launchpad.net/ubuntu/+source/glibc/+bug/1869364). Would a fix be for _dl_start_user to update _dl_auxv in the same way it updates _dl_argv? Or is that just naive (start up code confuses me!)
(In reply to Michael Hudson-Doyle from comment #2) > I've just run into this because it causes a glibc test failure when > libnss-systemd is enabled > (https://bugs.launchpad.net/ubuntu/+source/glibc/+bug/1869364). > > Would a fix be for _dl_start_user to update _dl_auxv in the same way it > updates _dl_argv? Or is that just naive (start up code confuses me!) I think this should work. There does not seems to be anything that stores the address if auxv entries, only values read from the vector.
(In reply to Florian Weimer from comment #3) > (In reply to Michael Hudson-Doyle from comment #2) > > I've just run into this because it causes a glibc test failure when > > libnss-systemd is enabled > > (https://bugs.launchpad.net/ubuntu/+source/glibc/+bug/1869364). > > > > Would a fix be for _dl_start_user to update _dl_auxv in the same way it > > updates _dl_argv? Or is that just naive (start up code confuses me!) > > I think this should work. There does not seems to be anything that stores > the address if auxv entries, only values read from the vector. it may work, but i think _dl_start_user stack handling should not be updated, it should be removed: the logic is backwards: most targets have fragile asm for the rtld start code to shuffle around entries on the stack, but such shuffling can be done in c in the generic code (e.g. in dl_main). this would also fix the (imo security) bug that the protection of dl data is not consistent across targets (DL_ARGV_NOT_RELRO). and all this mess is for saving a few cycles on targets where you don't need to do the shuffling. i think the generic code should work for all targets and those who wish to optimize add some hacks (e.g. ifdef out the shuffling), not the other way around. i didnt get the chance to clean this up yet, so it's not fixed.
(In reply to Szabolcs Nagy from comment #4) > (In reply to Florian Weimer from comment #3) > > (In reply to Michael Hudson-Doyle from comment #2) > > > I've just run into this because it causes a glibc test failure when > > > libnss-systemd is enabled > > > (https://bugs.launchpad.net/ubuntu/+source/glibc/+bug/1869364). > > > > > > Would a fix be for _dl_start_user to update _dl_auxv in the same way it > > > updates _dl_argv? Or is that just naive (start up code confuses me!) > > > > I think this should work. There does not seems to be anything that stores > > the address if auxv entries, only values read from the vector. > > it may work, but i think _dl_start_user stack handling should > not be updated, it should be removed: the logic is backwards: > > most targets have fragile asm for the rtld start code to shuffle > around entries on the stack, but such shuffling can be done in c > in the generic code (e.g. in dl_main). > > this would also fix the (imo security) bug that the protection > of dl data is not consistent across targets (DL_ARGV_NOT_RELRO). > > and all this mess is for saving a few cycles on targets where > you don't need to do the shuffling. i think the generic code > should work for all targets and those who wish to optimize > add some hacks (e.g. ifdef out the shuffling), not the other > way around. > > i didnt get the chance to clean this up yet, so it's not fixed. That sounds of course very reasonable. As long as very manipulate the arguments as arrays, the C code should be very portable. An assembler stub will still be needed, but it will be much smaller. I also think we should move the assembler code out of dl-machine.h while we are at it. We can start out with an empty dl-start.S file, and gradually move ports to follow the powerpc32 example.
I believe this is causing dlfcn/tst-dlinfo-phdr to fail in some cases.
The master branch has been updated by Szabolcs Nagy <nsz@sourceware.org>: https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=ad43cac44a6860eaefcadadfb2acb349921e96bf commit ad43cac44a6860eaefcadadfb2acb349921e96bf Author: Szabolcs Nagy <szabolcs.nagy@arm.com> Date: Fri Jun 15 16:14:58 2018 +0100 rtld: Use generic argv adjustment in ld.so [BZ #23293] When an executable is invoked as ./ld.so [ld.so-args] ./exe [exe-args] then the argv is adujusted in ld.so before calling the entry point of the executable so ld.so args are not visible to it. On most targets this requires moving argv, env and auxv on the stack to ensure correct stack alignment at the entry point. This had several issues: - The code for this adjustment on the stack is written in asm as part of the target specific ld.so _start code which is hard to maintain. - The adjustment is done after _dl_start returns, where it's too late to update GLRO(dl_auxv), as it is already readonly, so it points to memory that was clobbered by the adjustment. This is bug 23293. - _environ is also wrong in ld.so after the adjustment, but it is likely not used after _dl_start returns so this is not user visible. - _dl_argv was updated, but for this it was moved out of relro, which changes security properties across targets unnecessarily. This patch introduces a generic _dl_start_args_adjust function that handles the argument adjustments after ld.so processed its own args and before relro protection is applied. The same algorithm is used on all targets, _dl_skip_args is now 0, so existing target specific adjustment code is no longer used. The bug affects aarch64, alpha, arc, arm, csky, ia64, nios2, s390-32 and sparc, other targets don't need the change in principle, only for consistency. The GNU Hurd start code relied on _dl_skip_args after dl_main returned, now it checks directly if args were adjusted and fixes the Hurd startup data accordingly. Follow up patches can remove _dl_skip_args and DL_ARGV_NOT_RELRO. Tested on aarch64-linux-gnu and cross tested on i686-gnu. Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
The master branch has been updated by Szabolcs Nagy <nsz@sourceware.org>: https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=9faf5262c77487c96da8a3e961b88c0b1879e186 commit 9faf5262c77487c96da8a3e961b88c0b1879e186 Author: Szabolcs Nagy <szabolcs.nagy@arm.com> Date: Tue May 3 13:18:04 2022 +0100 linux: Add a getauxval test [BZ #23293] This is for bug 23293 and it relies on the glibc test system running tests via explicit ld.so invokation by default. Reviewed-by: Florian Weimer <fweimer@redhat.com> Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
fixed for 2.36.
The release/2.35/master branch has been updated by Szabolcs Nagy <nsz@sourceware.org>: https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=f5f7144dfcbf2a11fd2c17316c213928307c1db3 commit f5f7144dfcbf2a11fd2c17316c213928307c1db3 Author: Szabolcs Nagy <szabolcs.nagy@arm.com> Date: Fri Jun 15 16:14:58 2018 +0100 rtld: Use generic argv adjustment in ld.so [BZ #23293] When an executable is invoked as ./ld.so [ld.so-args] ./exe [exe-args] then the argv is adujusted in ld.so before calling the entry point of the executable so ld.so args are not visible to it. On most targets this requires moving argv, env and auxv on the stack to ensure correct stack alignment at the entry point. This had several issues: - The code for this adjustment on the stack is written in asm as part of the target specific ld.so _start code which is hard to maintain. - The adjustment is done after _dl_start returns, where it's too late to update GLRO(dl_auxv), as it is already readonly, so it points to memory that was clobbered by the adjustment. This is bug 23293. - _environ is also wrong in ld.so after the adjustment, but it is likely not used after _dl_start returns so this is not user visible. - _dl_argv was updated, but for this it was moved out of relro, which changes security properties across targets unnecessarily. This patch introduces a generic _dl_start_args_adjust function that handles the argument adjustments after ld.so processed its own args and before relro protection is applied. The same algorithm is used on all targets, _dl_skip_args is now 0, so existing target specific adjustment code is no longer used. The bug affects aarch64, alpha, arc, arm, csky, ia64, nios2, s390-32 and sparc, other targets don't need the change in principle, only for consistency. The GNU Hurd start code relied on _dl_skip_args after dl_main returned, now it checks directly if args were adjusted and fixes the Hurd startup data accordingly. Follow up patches can remove _dl_skip_args and DL_ARGV_NOT_RELRO. Tested on aarch64-linux-gnu and cross tested on i686-gnu. Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org> (cherry picked from commit ad43cac44a6860eaefcadadfb2acb349921e96bf)
The release/2.35/master branch has been updated by Szabolcs Nagy <nsz@sourceware.org>: https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=2b128a7d30f5f808c5246034f71d249010521f1b commit 2b128a7d30f5f808c5246034f71d249010521f1b Author: Szabolcs Nagy <szabolcs.nagy@arm.com> Date: Tue May 3 13:18:04 2022 +0100 linux: Add a getauxval test [BZ #23293] This is for bug 23293 and it relies on the glibc test system running tests via explicit ld.so invokation by default. Reviewed-by: Florian Weimer <fweimer@redhat.com> Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org> (cherry picked from commit 9faf5262c77487c96da8a3e961b88c0b1879e186)
The release/2.34/master branch has been updated by Szabolcs Nagy <nsz@sourceware.org>: https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=c73c79af7d6f1124fbfa5d935b4f620217d6a2ec commit c73c79af7d6f1124fbfa5d935b4f620217d6a2ec Author: Szabolcs Nagy <szabolcs.nagy@arm.com> Date: Fri Jun 15 16:14:58 2018 +0100 rtld: Use generic argv adjustment in ld.so [BZ #23293] When an executable is invoked as ./ld.so [ld.so-args] ./exe [exe-args] then the argv is adujusted in ld.so before calling the entry point of the executable so ld.so args are not visible to it. On most targets this requires moving argv, env and auxv on the stack to ensure correct stack alignment at the entry point. This had several issues: - The code for this adjustment on the stack is written in asm as part of the target specific ld.so _start code which is hard to maintain. - The adjustment is done after _dl_start returns, where it's too late to update GLRO(dl_auxv), as it is already readonly, so it points to memory that was clobbered by the adjustment. This is bug 23293. - _environ is also wrong in ld.so after the adjustment, but it is likely not used after _dl_start returns so this is not user visible. - _dl_argv was updated, but for this it was moved out of relro, which changes security properties across targets unnecessarily. This patch introduces a generic _dl_start_args_adjust function that handles the argument adjustments after ld.so processed its own args and before relro protection is applied. The same algorithm is used on all targets, _dl_skip_args is now 0, so existing target specific adjustment code is no longer used. The bug affects aarch64, alpha, arc, arm, csky, ia64, nios2, s390-32 and sparc, other targets don't need the change in principle, only for consistency. The GNU Hurd start code relied on _dl_skip_args after dl_main returned, now it checks directly if args were adjusted and fixes the Hurd startup data accordingly. Follow up patches can remove _dl_skip_args and DL_ARGV_NOT_RELRO. Tested on aarch64-linux-gnu and cross tested on i686-gnu. Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org> (cherry picked from commit ad43cac44a6860eaefcadadfb2acb349921e96bf)
The release/2.34/master branch has been updated by Szabolcs Nagy <nsz@sourceware.org>: https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=b2585cae2854d7d2868fb2e51e2796042c5e0679 commit b2585cae2854d7d2868fb2e51e2796042c5e0679 Author: Szabolcs Nagy <szabolcs.nagy@arm.com> Date: Tue May 3 13:18:04 2022 +0100 linux: Add a getauxval test [BZ #23293] This is for bug 23293 and it relies on the glibc test system running tests via explicit ld.so invokation by default. Reviewed-by: Florian Weimer <fweimer@redhat.com> Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org> (cherry picked from commit 9faf5262c77487c96da8a3e961b88c0b1879e186)