mirror of
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
synced 2026-05-23 10:16:50 -04:00
7e1088760c
Anatoly reports that since commit:ff5b4f1ed5("locking/atomic: sparc: move to ARCH_ATOMIC") ... it's possible to reliably trigger an oops by running: stress-ng -v --mmap 1 -t 30s ... which results in a NULL pointer dereference in __split_huge_pmd_locked(). The underlying problem is that commitff5b4f1ed5left arch_cmpxchg64_local() defined in terms of cmpxchg_local() rather than arch_cmpxchg_local(). In <asm-generic/atomic-instrumented.h> we wrap these with macros which use identically-named variables. When cmpxchg_local() nests inside cmpxchg64_local(), this casues it to use an unitialized variable as the pointer, which can be NULL. This can also be seen in pmdp_establish(), where the compiler can generate the pointer with a `clr` instruction: 0000000000000360 <pmdp_establish>: 360: 9d e3 bf 50 save %sp, -176, %sp 364: fa 5e 80 00 ldx [ %i2 ], %i5 368: 82 10 00 1b mov %i3, %g1 36c: 84 10 20 00 clr %g2 370: c3 f0 90 1d casx [ %g2 ], %i5, %g1 374: 80 a7 40 01 cmp %i5, %g1 378: 32 6f ff fc bne,a %xcc, 368 <pmdp_establish+0x8> 37c: fa 5e 80 00 ldx [ %i2 ], %i5 380: d0 5e 20 40 ldx [ %i0 + 0x40 ], %o0 384: 96 10 00 1b mov %i3, %o3 388: 94 10 00 1d mov %i5, %o2 38c: 92 10 00 19 mov %i1, %o1 390: 7f ff ff 84 call 1a0 <__set_pmd_acct> 394: b0 10 00 1d mov %i5, %i0 398: 81 cf e0 08 return %i7 + 8 39c: 01 00 00 00 nop This patch fixes the problem by defining arch_cmpxchg64_local() in terms of arch_cmpxchg_local(), avoiding potential shadowing, and resulting in working cmpxchg64_local() and variants, e.g. 0000000000000360 <pmdp_establish>: 360: 9d e3 bf 50 save %sp, -176, %sp 364: fa 5e 80 00 ldx [ %i2 ], %i5 368: 82 10 00 1b mov %i3, %g1 36c: c3 f6 90 1d casx [ %i2 ], %i5, %g1 370: 80 a7 40 01 cmp %i5, %g1 374: 32 6f ff fd bne,a %xcc, 368 <pmdp_establish+0x8> 378: fa 5e 80 00 ldx [ %i2 ], %i5 37c: d0 5e 20 40 ldx [ %i0 + 0x40 ], %o0 380: 96 10 00 1b mov %i3, %o3 384: 94 10 00 1d mov %i5, %o2 388: 92 10 00 19 mov %i1, %o1 38c: 7f ff ff 85 call 1a0 <__set_pmd_acct> 390: b0 10 00 1d mov %i5, %i0 394: 81 cf e0 08 return %i7 + 8 398: 01 00 00 00 nop 39c: 01 00 00 00 nop Fixes:ff5b4f1ed5("locking/atomic: sparc: move to ARCH_ATOMIC") Reported-by: Anatoly Pugachev <matorola@gmail.com> Signed-off-by: Mark Rutland <mark.rutland@arm.com> Signed-off-by: Ingo Molnar <mingo@kernel.org> Tested-by: Anatoly Pugachev <matorola@gmail.com> Link: https://lore.kernel.org/r/20210707083032.567-1-mark.rutland@arm.com
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.