{"push_id":2920248867,"size":1,"distinct_size":1,"ref":"refs/heads/powerpc_nohash_fix_undefined_behaviour_when_testing_page_size_support_mbox_next","head":"5f22a793c602b8a1102447c5faef038a1f3b7de2","before":"fdf8c1544af51d8bfed8de8e41faf2049533ce9f","commits":[{"sha":"5f22a793c602b8a1102447c5faef038a1f3b7de2","author":{"name":"Daniel Axtens","email":"cf1af486034ab0119a20f38a060e40da25f4cea3@axtens.net"},"message":"powerpc/nohash: fix undefined behaviour when testing page size support\n\nWhen enumerating page size definitions to check hardware support,\nwe construct a constant which is (1U << (def->shift - 10)).\n\nHowever, the array of page size definitions is only initalised for\nvarious MMU_PAGE_* constants, so it contains a number of 0-initialised\nelements with def->shift == 0. This means we end up shifting by a\nvery large number, which gives the following UBSan splat:\n\n================================================================================\nUBSAN: Undefined behaviour in /home/dja/dev/linux/linux/arch/powerpc/mm/tlb_nohash.c:506:21\nshift exponent 4294967286 is too large for 32-bit type 'unsigned int'\nCPU: 0 PID: 0 Comm: swapper Not tainted 4.19.0-rc3-00045-ga604f927b012-dirty #6\nCall Trace:\n[c00000000101bc20] [c000000000a13d54] .dump_stack+0xa8/0xec (unreliable)\n[c00000000101bcb0] [c0000000004f20a8] .ubsan_epilogue+0x18/0x64\n[c00000000101bd30] [c0000000004f2b10] .__ubsan_handle_shift_out_of_bounds+0x110/0x1a4\n[c00000000101be20] [c000000000d21760] .early_init_mmu+0x1b4/0x5a0\n[c00000000101bf10] [c000000000d1ba28] .early_setup+0x100/0x130\n[c00000000101bf90] [c000000000000528] start_here_multiplatform+0x68/0x80\n================================================================================\n\nFix this by first checking if the element exists (shift != 0) before\nconstructing the constant.\n\nSigned-off-by: Daniel Axtens <dja@axtens.net>","distinct":true,"url":"https://api.github.com/repos/ruscur/linux/commits/5f22a793c602b8a1102447c5faef038a1f3b7de2"}]}
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