As always, Linus hasn’t ceased to surprise us with his love for Linux . Linus Torvald promised a Linux Kernel candidate by the new year. To our utter surprise, he released it a day before Christmas.

Linux Kernel RC 4.15

Linux Kernel 4.15

After 200 iterations in two months, the Linux Kernel RC 4.15 is a big update. Recently there have been a few attacks which put linux on the mark as well, like the wpa attack.

The Linux kernel is the soul ofĀ any Linux operating system. It is core responsibilities includes

  • Resource allocation

  • Low-level hardware interfacing

  • Security

  • Simple communications

  • Basic file system management and much more.

A day before Christmas, Linus Torvald announced 5th released candidate (RC) Linux kernel 4.15 for testing. New Linux Kernel is a big news because unlike Windows, The Linux gets a new kernel in years. Mostly because it doesn’t require many core updates.

Linux was launched in 1991; since then this is 14th Linux Kernel since the inception of original Linux Kernel 0.01 in the year 1991.

This, however, according to Linus is a normal update. Only big change in the Linux Kernel 4.15 RC5 from its predecessor is that it has x86 low – level preparation for kernel page table isolation.

Features of Linux Kernel 4.15 RC

Linux Kernel RC 4.15 has many small features that will make our lives a little easier with Linux. Following are the updates that are rolled out for testing 4.15 RC Linux Kernel.

The x86 Update

There are about 48 x86 updates, the major updates include Stack Overflow on all stack, Improved Memory Map documentation, remap TSS into CPU entry area.

A new function in dumpstackĀ  get_stack_info() support for SYSENTER stack. There are many minor updates that make the core more stable and developer friendly.

x86/cpu_entry_area Move it out of the fixmap
x86/cpu_entry_area Move it to a separate unit
x86/cpu_entry_area Prevent wraparound in KVM

x86/cpufeatures Make CPU bugs sticky
x86/doc Remove obvious weirdnesses from the x86 MM layout documentation

x86/espfix/64 Stop assuming that pt_regs is on the entry stack

x86/dumpstack Add get_stack_info() support for the SYSENTER stack
x86/dumpstack Handle stack overflow on all stacks

x86/entry Clean up the SYSENTER_stack code
x86/entry Fix assumptions that the HW TSS is at the beginning of cpu_tss
x86/entry Move SYSENTER_stack to the beginning of struct tss_struct
x86/entry Remap the TSS into the CPU entry area
x86/entry/64 Allocate and enable the SYSENTER stack
x86/entry/64 Create a per-CPU SYSCALL entry trampoline
x86/entry/64 Make cpu_entry_area.tss read-only
x86/entry/64 Move the IST stacks into struct cpu_entry_area
x86/entry/64 Remove the SYSENTER stack canary
x86/entry/64 Return to userspace from the trampoline stack
x86/entry/64 Separate cpu_current_top_of_stack from TSS.sp0
x86/entry/64 Use a per-CPU trampoline stack for IDT entries
x86/entry/gdt Put per-CPU GDT remaps in ascending order

x86/irq Remove an old outdated comment about context tracking races
x86/irq/64 Print the offending IP in the stack overflow warning
x86/kasan/64 Teach KASAN about the cpu_entry_area
x86/Kconfig Limit NR_CPUS on 32-bit to a sane amount
x86/ldt Prevent LDT inheritance on exec
x86/microcode Don’t abuse the TLB-flush interface

x86/mm Add comments to clarify which TLB-flush functions are
x86/mm Create asm/invpcid.h
x86/mm Move the CR3 construction functions to tlbflush.h
x86/mm Put MMU to hardware ASID translation in one place
x86/mm Remove hard-coded ASID limit checks
x86/mm Remove superfluous barriers
x86/mm Use __flush_tlb_one() for kernel memory
x86/mm/64 Improve the memory map documentation
x86/mm/dump_pagetables Check PAGE_PRESENT for real
x86/mm/dump_pagetables Make the address hints correct and readable
x86/mm/fixmap Generalize the GDT fixmap mechanism, introduce struct cpu_entry_area

x86/paravirt Provide a way to check for hypervisors
x86/uv Use the right TLB-flush API
x86/vsyscall/64 Explicitly set _PAGE_USER in the pagetable hierarchy
x86/vsyscall/64 Warn and fail vsyscall emulation in NATIVE mode

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Driver Updates

There are many driver updates that will increase the horizon for the development and usage forĀ Linux kernel 6 that is set for release in 2018.

Berkely Packet Filters (BPF)

BPF is a module that provides an interface to Data Link Layers. It is a common module available in many UNIX-like OS. There are few BFP updates that stand out in this release.

bpf: fix integer overflows
bpf: do not allow root to mangle valid pointers
bpf: s390x: do not reload skb pointers in non-skb context
bpf: ppc64: do not reload skb pointers in non-skb context
bpf: guarantee r1 to be ctx in case of bpf_helper_changes_pkt_data
bpf: sparc: fix usage of wrong reg for load_skb_regs after call
bpf: add test case for ld_abs and helper changing pkt data
bpf: Fix tools and testing build.
bpf/verifier: fix bounds calculation on BPF_RSH
bpf: fix broken BPF selftest build on s390
cls_bpf: fix offload assumptions after callback conversion
bpf: keep track of the offloaded program
bpf: fix incorrect sign extension in check_alu_op()
bpf: fix incorrect tracking of register size truncation
bpf: fix 32-bit ALU op verification
bpf: fix missing error return in check_stack_boundary()
bpf: force strict alignment checks for stack pointers
bpf: don’t prune branches when a scalar is replaced with a pointer
selftests/bpf: add tests for recent bugfixes


Following are the updates in selftest

selftests/bpf: fix broken BPF selftest build on s390
selftests/bpf: add tests for recent bugfixes
selftests: net: Adding config fragment CONFIG_NUMA=y

XFS File System updates

There are total 15 updates in XFS.

xfs: add the ability to join a held buffer to a defer_ops
xfs: hold xfs_buf locked between shortform->leaf conversion and the addition of an attribute
xfs: account for null transactions in bunmapi
xfs: move xfs_iext_insert tracepoint to report useful information
xfs: remove dest file’s post-eof preallocations before reflinking
xfs: relax is_reflink_inode assert in xfs_reflink_find_cow_mapping
xfs: avoid infinite loop when cancelling CoW blocks after writeback failure
xfs: allow CoW remap transactions to use reserve blocks
xfs: track cowblocks separately in i_flags
xfs: don’t be so eager to clear the cowblocks tag on truncate
xfs: remove leftover CoW reservations when remounting ro
xfs: set cowblocks tag for direct cow writes too
xfs: queue deferred rmap ops for cow staging extent alloc/free in the right order
xfs: always honor OWN_UNKNOWN rmap removal requests
xfs: only skip rmap owner checks for unknown-owner rmap removal

If you want to test the latest RC, you can do so by downloading the Linux kernel 4.15 RC5 source from or from softpedia.Keep yourself updated with latest developments of Tech world, followĀ Techscoop.inonĀ Facebook,Ā TwitterĀ andĀ Google+.

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