On Mon, Aug 07, 2017 at 08:16:10PM +0200, Marc-André Lureau wrote: > Recent linux kernels enable KASLR to randomize phys/virt memory > addresses. This series aims to provide enough information in qemu > dumps so that crash utility can work with randomized kernel too (it > hasn't been tested on other archs than x86 though, help welcome). > > The previous design to provide qemu with debug details (using qemu-ga > and a dedicated vmcoreinfo ACPI device) failed to satisfy the > requirements during previous iterations. > > In particular, the previous proposed vmcoreinfo ACPI device had the > following issues: > - hazardous memory handling with no explicit synchronization > - occupy 2 fw-cfg entries (for memory and pointer) > - occupy 4k of guest memory (this could have been tweaked) > - did not provide ACPI methods (this could have been added) > - may be difficult to maintain compatibility (according to Michael) > > This is a new proposal, that leverage fw-cfg device instead of adding > a new device. A "etc/vmcoreinfo" entry is added, where the guest, > during boot or later, can write the addr/size location of an ELF note > to be appended in the qemu dump.
Looks ok to me. Pls remember to ping after release. > Note: only guest kernel is expected to write to a fw-cfg entry. This > method is not meant for general qemu/user-space communication. There > are more appropriate devices for this purpose, and the guest kernel > should not expose this facility. > > This is quite easier to implement, and uses less of the limited fw-cfg > slots, and guest memory. It also solves the synchronization issue, and > may be easier to discover or to maintain compatibility. > > The Linux ELF note is expected to be the VMCOREINFO note, which will > have a special handling in qemu in this case helping kaslr-kernel > debugging. But it could be any valid ELF note. > > Crash 7.1.9 will parse the "phys_base" value from the VMCOREINFO note, > and thus will work with KASLR-dump produced by this series. > > The series implements the note addition in qemu ELF/kdump, > as well as the python scripts/dump-guest-memory.py. > > To test: > > Using kernel from https://github.com/elmarco/linux fw-cfg branch, > Compile and run guest kernel with CONFIG_RANDOMIZE_BASE=y & > CONFIG_FW_CFG_SYSFS=y. > > Run qemu with -global fw_cfg.vmcoreinfo=on > > Produce an ELF dump: > { "execute": "dump-guest-memory", "arguments": { "protocol": "file:dump", > "paging": false } } > > Produce a kdump: > { "execute": "dump-guest-memory", "arguments": { "protocol": "file:dump", > "paging": false, "format": "kdump-zlib" } } > > Or with (gdb) dump-guest-memory, with scripts/dump-guest-memory.py script. > > Analyze with crash >= 7.1.9 (or the git version for 4.13 fixes..): > > $ crash vmlinux dump > > v5: > - removed x-write-pointer-available patch from this series > - drop vmcoreinfo device > - add write callback to fw_cfg entries > - add a writable fw_cfg "vmcoreinfo" entry > - split phys_base update from VMCOREINFO note in a seperate patch > - most patches had non-trivial changes, dropping reviewed-by tags > > v4: from Laszlo review > - switch to warn_report*() > - update test to follow vmgenid and use boot-sector infrastructure > - fix range checks in the python script > - add vmcoreinfo_get() stub > > v3: from Laszlo review > - change vmcoreinfo offset to 36 > - reset err to null after report > - use PRIu32 > - change name_size and desc_size against MAX_VMCOREINFO_SIZE > - python code simplification > - check boundaries of blocks in phys_memory_read() > - fix some vmgi vs vmci names > - add more comments in code > - fix comment indentation > - add r-b tags > > v2: from Laszlo review > - vmci: fix guest endianess handling > - vmci: fix wrong sizeof() > - vmci: add back reset logic from vmgenid > - dump: have 1MB size limit for vmcoreinfo > - dump: fix potential off-by-1 buffer manipulation > - dump: use temporary variable for qemu_strtou64 > - dump: fixed VMCOREINFO duplication in kdump > - update gdb script to not call into qemu process > - update MAINTAINERS with some new files > > Marc-André Lureau (8): > fw_cfg: rename read callback > fw_cfg: add write callback > fw_cfg: add vmcoreinfo file > dump: add guest ELF note > dump: update phys_base header field based on VMCOREINFO content > kdump: set vmcoreinfo location > scripts/dump-guest-memory.py: add vmcoreinfo > MAINTAINERS: add Dump maintainers > > scripts/dump-guest-memory.py | 51 ++++++++++++ > include/hw/compat.h | 8 ++ > include/hw/loader.h | 2 +- > include/hw/nvram/fw_cfg.h | 18 ++++- > include/sysemu/dump.h | 2 + > dump.c | 179 > +++++++++++++++++++++++++++++++++++++++++++ > hw/acpi/vmgenid.c | 2 +- > hw/core/loader.c | 4 +- > hw/i386/acpi-build.c | 2 +- > hw/isa/lpc_ich9.c | 4 +- > hw/nvram/fw_cfg.c | 64 ++++++++++++---- > MAINTAINERS | 9 +++ > docs/specs/fw_cfg.txt | 24 ++++++ > 13 files changed, 343 insertions(+), 26 deletions(-) > > -- > 2.14.0.1.geff633fa0
