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Mon, 10 Feb 2025 14:23:09 -0800 (PST) Message-ID: <55f44ab1-25ed-4756-8621-162e02471fda@citrix.com> Date: Mon, 10 Feb 2025 22:23:07 +0000 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH for-4.20? 1/4] ARM32/traps: Fix do_trap_undefined_instruction()'s detection of kernel text To: Julien Grall , Xen-devel Cc: Stefano Stabellini , Volodymyr Babchuk , Bertrand Marquis , Michal Orzel , Oleksii Kurochko References: <20250208000256.431883-1-andrew.cooper3@citrix.com> <20250208000256.431883-2-andrew.cooper3@citrix.com> <34c2dc12-eb49-4c16-97b5-166b889822a2@xen.org> Content-Language: en-GB From: Andrew Cooper Autocrypt: addr=andrew.cooper3@citrix.com; keydata= xsFNBFLhNn8BEADVhE+Hb8i0GV6mihnnr/uiQQdPF8kUoFzCOPXkf7jQ5sLYeJa0cQi6Penp VtiFYznTairnVsN5J+ujSTIb+OlMSJUWV4opS7WVNnxHbFTPYZVQ3erv7NKc2iVizCRZ2Kxn srM1oPXWRic8BIAdYOKOloF2300SL/bIpeD+x7h3w9B/qez7nOin5NzkxgFoaUeIal12pXSR Q354FKFoy6Vh96gc4VRqte3jw8mPuJQpfws+Pb+swvSf/i1q1+1I4jsRQQh2m6OTADHIqg2E ofTYAEh7R5HfPx0EXoEDMdRjOeKn8+vvkAwhviWXTHlG3R1QkbE5M/oywnZ83udJmi+lxjJ5 YhQ5IzomvJ16H0Bq+TLyVLO/VRksp1VR9HxCzItLNCS8PdpYYz5TC204ViycobYU65WMpzWe LFAGn8jSS25XIpqv0Y9k87dLbctKKA14Ifw2kq5OIVu2FuX+3i446JOa2vpCI9GcjCzi3oHV e00bzYiHMIl0FICrNJU0Kjho8pdo0m2uxkn6SYEpogAy9pnatUlO+erL4LqFUO7GXSdBRbw5 gNt25XTLdSFuZtMxkY3tq8MFss5QnjhehCVPEpE6y9ZjI4XB8ad1G4oBHVGK5LMsvg22PfMJ ISWFSHoF/B5+lHkCKWkFxZ0gZn33ju5n6/FOdEx4B8cMJt+cWwARAQABzSlBbmRyZXcgQ29v cGVyIDxhbmRyZXcuY29vcGVyM0BjaXRyaXguY29tPsLBegQTAQgAJAIbAwULCQgHAwUVCgkI CwUWAgMBAAIeAQIXgAUCWKD95wIZAQAKCRBlw/kGpdefoHbdD/9AIoR3k6fKl+RFiFpyAhvO 59ttDFI7nIAnlYngev2XUR3acFElJATHSDO0ju+hqWqAb8kVijXLops0gOfqt3VPZq9cuHlh IMDquatGLzAadfFx2eQYIYT+FYuMoPZy/aTUazmJIDVxP7L383grjIkn+7tAv+qeDfE+txL4 SAm1UHNvmdfgL2/lcmL3xRh7sub3nJilM93RWX1Pe5LBSDXO45uzCGEdst6uSlzYR/MEr+5Z JQQ32JV64zwvf/aKaagSQSQMYNX9JFgfZ3TKWC1KJQbX5ssoX/5hNLqxMcZV3TN7kU8I3kjK mPec9+1nECOjjJSO/h4P0sBZyIUGfguwzhEeGf4sMCuSEM4xjCnwiBwftR17sr0spYcOpqET ZGcAmyYcNjy6CYadNCnfR40vhhWuCfNCBzWnUW0lFoo12wb0YnzoOLjvfD6OL3JjIUJNOmJy RCsJ5IA/Iz33RhSVRmROu+TztwuThClw63g7+hoyewv7BemKyuU6FTVhjjW+XUWmS/FzknSi dAG+insr0746cTPpSkGl3KAXeWDGJzve7/SBBfyznWCMGaf8E2P1oOdIZRxHgWj0zNr1+ooF /PzgLPiCI4OMUttTlEKChgbUTQ+5o0P080JojqfXwbPAyumbaYcQNiH1/xYbJdOFSiBv9rpt TQTBLzDKXok86M7BTQRS4TZ/ARAAkgqudHsp+hd82UVkvgnlqZjzz2vyrYfz7bkPtXaGb9H4 Rfo7mQsEQavEBdWWjbga6eMnDqtu+FC+qeTGYebToxEyp2lKDSoAsvt8w82tIlP/EbmRbDVn 7bhjBlfRcFjVYw8uVDPptT0TV47vpoCVkTwcyb6OltJrvg/QzV9f07DJswuda1JH3/qvYu0p vjPnYvCq4NsqY2XSdAJ02HrdYPFtNyPEntu1n1KK+gJrstjtw7KsZ4ygXYrsm/oCBiVW/OgU g/XIlGErkrxe4vQvJyVwg6YH653YTX5hLLUEL1NS4TCo47RP+wi6y+TnuAL36UtK/uFyEuPy wwrDVcC4cIFhYSfsO0BumEI65yu7a8aHbGfq2lW251UcoU48Z27ZUUZd2Dr6O/n8poQHbaTd 6bJJSjzGGHZVbRP9UQ3lkmkmc0+XCHmj5WhwNNYjgbbmML7y0fsJT5RgvefAIFfHBg7fTY/i kBEimoUsTEQz+N4hbKwo1hULfVxDJStE4sbPhjbsPCrlXf6W9CxSyQ0qmZ2bXsLQYRj2xqd1 bpA+1o1j2N4/au1R/uSiUFjewJdT/LX1EklKDcQwpk06Af/N7VZtSfEJeRV04unbsKVXWZAk uAJyDDKN99ziC0Wz5kcPyVD1HNf8bgaqGDzrv3TfYjwqayRFcMf7xJaL9xXedMcAEQEAAcLB XwQYAQgACQUCUuE2fwIbDAAKCRBlw/kGpdefoG4XEACD1Qf/er8EA7g23HMxYWd3FXHThrVQ HgiGdk5Yh632vjOm9L4sd/GCEACVQKjsu98e8o3ysitFlznEns5EAAXEbITrgKWXDDUWGYxd pnjj2u+GkVdsOAGk0kxczX6s+VRBhpbBI2PWnOsRJgU2n10PZ3mZD4Xu9kU2IXYmuW+e5KCA vTArRUdCrAtIa1k01sPipPPw6dfxx2e5asy21YOytzxuWFfJTGnVxZZSCyLUO83sh6OZhJkk b9rxL9wPmpN/t2IPaEKoAc0FTQZS36wAMOXkBh24PQ9gaLJvfPKpNzGD8XWR5HHF0NLIJhgg 4ZlEXQ2fVp3XrtocHqhu4UZR4koCijgB8sB7Tb0GCpwK+C4UePdFLfhKyRdSXuvY3AHJd4CP 4JzW0Bzq/WXY3XMOzUTYApGQpnUpdOmuQSfpV9MQO+/jo7r6yPbxT7CwRS5dcQPzUiuHLK9i nvjREdh84qycnx0/6dDroYhp0DFv4udxuAvt1h4wGwTPRQZerSm4xaYegEFusyhbZrI0U9tJ B8WrhBLXDiYlyJT6zOV2yZFuW47VrLsjYnHwn27hmxTC/7tvG3euCklmkn9Sl9IAKFu29RSo d5bD8kMSCYsTqtTfT6W4A3qHGvIDta3ptLYpIAOD2sY3GYq2nf3Bbzx81wZK14JdDDHUX2Rs 6+ahAA== In-Reply-To: <34c2dc12-eb49-4c16-97b5-166b889822a2@xen.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On 10/02/2025 9:23 pm, Julien Grall wrote: > Hi Andrew, > > On 08/02/2025 00:02, Andrew Cooper wrote: >> While fixing some common/arch boundaries for UBSAN support on other >> architectures, the following debugging patch: >> >>    diff --git a/xen/arch/arm/setup.c b/xen/arch/arm/setup.c >>    index c1f2d1b89d43..58d1d048d339 100644 >>    --- a/xen/arch/arm/setup.c >>    +++ b/xen/arch/arm/setup.c >>    @@ -504,6 +504,8 @@ void asmlinkage __init start_xen(unsigned long >> fdt_paddr) >> >>         system_state = SYS_STATE_active; >> >>    +    dump_execution_state(); >>    + >>         for_each_domain( d ) >>             domain_unpause_by_systemcontroller(d); >> >> fails with: >> >>    (XEN) *** Serial input to DOM0 (type 'CTRL-a' three times to >> switch input) >>    (XEN) CPU0: Unexpected Trap: Undefined Instruction >>    (XEN) ----[ Xen-4.20-rc  arm32  debug=n  Not tainted ]---- >>    (XEN) CPU:    0 >>    >>    (XEN) >>    (XEN) **************************************** >>    (XEN) Panic on CPU 0: >>    (XEN) CPU0: Unexpected Trap: Undefined Instruction >>    (XEN) **************************************** >> >> This is because the condition for init text is wrong.  While there's >> nothing >> interesting from that point onwards in start_xen(), it's also wrong >> for any >> livepatch which brings in an adjusted BUG_FRAME(). >> >> Use is_active_kernel_text() which is the correct test for this >> purpose, and is >> aware of init and livepatch regions too. >> >> Commit c8d4b6304a5e ("xen/arm: add support for >> run_in_exception_handler()"), >> made run_in_exception_handler() work, but didn't complete the TODO >> left in >> commit 3e802c6ca1fb ("xen/arm: Correctly support WARN_ON").  Do so, >> to make >> ARM consistent with other architectures. > > This was done on purpose. If you look at the current implementation of > run_in_exception_handler(), it will clobber some registers. > > With your patch #2, the function should only clobber one. It is a bit > better, but it still not great. So I think we need to stick with > WARN() on Arm (+ maybe a comment explaning why it is implemented > differently). I'm sorry but I don't follow. run_in_exception_handler() only uses 1 register (after patch 2), but it's fully described to the invoking context, so nothing is clobbered from the compilers point of view. Are you concerned about losing r0/x0 in the resulting trace? I can certainly split the patch in half.  The do_trap_undefined_instruction() change isn't related, although the second hunk is needed for patch 3 to consolidate dump_execution_state() across architectures. ~Andrew