7fad2a432c
The shadow stack signal frame is read by the kernel on sigreturn. It relies on shadow stack memory protections to prevent forgeries of this signal frame (which included the pre-signal SSP). This behavior helps userspace protect itself. However, using the INCSSP instruction userspace can adjust the SSP to 8 bytes beyond the end of a shadow stack. INCSSP performs shadow stack reads to make sure it doesn’t increment off of the shadow stack, but on the end position it actually reads 8 bytes below the new SSP. For the shadow stack HW operations, this situation (INCSSP off the end of a shadow stack by 8 bytes) would be fine. If the a RET is executed, the push to the shadow stack would fail to write to the shadow stack. If a CALL is executed, the SSP will be incremented back onto the stack and the return address will be written successfully to the very end. That is expected behavior around shadow stack underflow. However, the kernel doesn’t have a way to read shadow stack memory using shadow stack accesses. WRUSS can write to shadow stack memory with a shadow stack access which ensures the access is to shadow stack memory. But unfortunately for this case, there is no equivalent instruction for shadow stack reads. So when reading the shadow stack signal frames, the kernel currently assumes the SSP is pointing to the shadow stack and uses a normal read. The SSP pointing to shadow stack memory will be true in most cases, but as described above, in can be untrue by 8 bytes. So lookup the VMA of the shadow stack sigframe being read to verify it is shadow stack. Since the SSP can only be beyond the shadow stack by 8 bytes, and shadow stack memory is page aligned, this check only needs to be done when this type of relative position to a page boundary is encountered. So skip the extra work otherwise. Signed-off-by: Rick Edgecombe <rick.p.edgecombe@intel.com> Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com> Link: https://lore.kernel.org/all/20230613001108.3040476-34-rick.p.edgecombe%40intel.com |
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| Documentation | ||
| LICENSES | ||
| arch | ||
| block | ||
| certs | ||
| crypto | ||
| drivers | ||
| fs | ||
| include | ||
| init | ||
| io_uring | ||
| ipc | ||
| kernel | ||
| lib | ||
| mm | ||
| net | ||
| rust | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .cocciconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| .rustfmt.toml | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
| Kconfig | ||
| MAINTAINERS | ||
| Makefile | ||
| README | ||
README
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.