Messages in this thread | ![/](/images/icornerl.gif) | | Date | Mon, 26 Jun 2023 22:49:44 +0200 | From | Sebastian Sumpf <> | Subject | [Bug report] __arch_hweight32/64 x86 |
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Hello kernel developers,
I recently stumbled over a bug in the inline assembly of '__arch_hweight32' and '__arch_hweight64' in 'arch/x86/include/asm/arch_hweight.h' (present in 6.4 as well):
! asm (ALTERNATIVE("call __sw_hweight64", "popcntq %1, %0", ! X86_FEATURE_POPCNT) ! : "="REG_OUT (res) ! : REG_IN (w));
The 'ALTERNATIVE' macro checks for the popcnt feature. In case this fails the '__sw_hweight' C-function is called from inline assembly with rax and rdi as intput/output operands. However, the code does not contain a clobber list of any callee safe registers that might be touched by the '__sw_height64' C-function. Therefore, these registers will not be restored upon function return by the compiler. This leads to varying exceptions/bad behavior caused by the thus corrupted registers later on.
Kind regards,
Sebastian
-- Sebastian Sumpf Genode Labs
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