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AJvYcCX+RBMz2m8b4ajVdQuTHLFjSZcXgS7OkCCWnR2OYUUnup5WV8SmuUYNGf3iAJ0oh9gUCwstEf78nU0=@lists.xenproject.org X-Gm-Message-State: AOJu0YzxGuLp2PgfVHsCTxAdxx9BPRx1du37gPHdrjz+XrEX4+liq0Xb UIudpb2CJvq+FS1zrnLN8cmakUK0XKLcv3UiedvdtlGMciQT6aQZFYQV2hTXaX8= X-Google-Smtp-Source: AGHT+IEcL3FZzcZW//HkvhrwOlPaidcxVkBzd5xAmIKoOdPaFppZ+5ydreldNX+4B82kVxECt/ScbA== X-Received: by 2002:a05:6512:32c8:b0:536:54db:ddd0 with SMTP id 2adb3069b0e04-536ac179fdamr5740031e87.0.1727090273749; Mon, 23 Sep 2024 04:17:53 -0700 (PDT) Message-ID: Date: Mon, 23 Sep 2024 12:17:51 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 3/3] x86/alternatives: relax apply BUGs during runtime To: Roger Pau Monne , xen-devel@lists.xenproject.org Cc: Jan Beulich , Ross Lagerwall , =?UTF-8?Q?Roger_Pau_Monn=C3=A9?= References: <20240920093656.48879-1-roger.pau@citrix.com> <20240920093656.48879-5-roger.pau@citrix.com> 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: <20240920093656.48879-5-roger.pau@citrix.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On 20/09/2024 10:36 am, Roger Pau Monne wrote: > alternatives is used both at boot time, and when loading livepatch payloads. > While for the former it makes sense to panic, it's not useful for the later, as > for livepatches it's possible to fail to load the livepatch if alternatives > cannot be resolved and continue operating normally. > > Relax the BUGs in _apply_alternatives() to instead return an error code if > alternatives are applied after boot. > > Add a dummy livepatch test so the new logic can be assessed, with the change > applied the loading now fails with: > > alt table ffff82d040602024 -> ffff82d040602032 > livepatch: xen_alternatives_fail applying alternatives failed: -22 > > Signed-off-by: Roger Pau Monné > --- > xen/arch/x86/alternative.c | 29 ++++++++++++++++------ > xen/arch/x86/include/asm/alternative.h | 3 ++- > xen/common/livepatch.c | 10 +++++++- > xen/test/livepatch/Makefile | 5 ++++ > xen/test/livepatch/xen_alternatives_fail.c | 29 ++++++++++++++++++++++ > 5 files changed, 66 insertions(+), 10 deletions(-) > create mode 100644 xen/test/livepatch/xen_alternatives_fail.c > > diff --git a/xen/arch/x86/alternative.c b/xen/arch/x86/alternative.c > index 7824053c9d33..c0912cb12ea5 100644 > --- a/xen/arch/x86/alternative.c > +++ b/xen/arch/x86/alternative.c > @@ -174,10 +174,13 @@ extern void *const __initdata_cf_clobber_end[]; > * The caller will set the "force" argument to true for the final > * invocation, such that no CALLs/JMPs to NULL pointers will be left > * around. See also the further comment below. > + * > + * Note the function cannot fail if system_state < SYS_STATE_active, it would > + * panic instead. The return value is only meaningful for runtime usage. > */ > -static void init_or_livepatch _apply_alternatives(struct alt_instr *start, > - struct alt_instr *end, > - bool force) > +static int init_or_livepatch _apply_alternatives(struct alt_instr *start, > + struct alt_instr *end, > + bool force) > { > struct alt_instr *a, *base; > > @@ -198,9 +201,17 @@ static void init_or_livepatch _apply_alternatives(struct alt_instr *start, > uint8_t buf[MAX_PATCH_LEN]; > unsigned int total_len = a->orig_len + a->pad_len; > > - BUG_ON(a->repl_len > total_len); > - BUG_ON(total_len > sizeof(buf)); > - BUG_ON(a->cpuid >= NCAPINTS * 32); > +#define BUG_ON_BOOT(cond) \ > + if ( system_state < SYS_STATE_active ) \ > + BUG_ON(cond); \ > + else if ( cond ) \ > + return -EINVAL; > + > + BUG_ON_BOOT(a->repl_len > total_len); > + BUG_ON_BOOT(total_len > sizeof(buf)); > + BUG_ON_BOOT(a->cpuid >= NCAPINTS * 32); > + > +#undef BUG_ON_BOOT The "error handling" before was horrible and this isn't really any better. This function should always return int, printing more helpful info than that (a printk() says a thousand things better than a BUG()), and nmi_apply_alternatives can panic() rather than leaving these BUG()s here. As a tangent, the __must_check doesn't seem to have been applied to nmi_apply_alternatives(), but I'd suggest dropping the attribute; I don't think it adds much. > diff --git a/xen/test/livepatch/xen_alternatives_fail.c b/xen/test/livepatch/xen_alternatives_fail.c > new file mode 100644 > index 000000000000..01d289095a31 > --- /dev/null > +++ b/xen/test/livepatch/xen_alternatives_fail.c > @@ -0,0 +1,29 @@ > +/* > + * Copyright (c) 2024 Cloud Software Group. > + * > + */ > + > +#include "config.h" > +#include > +#include > + > +#include > +#include > + > +void test_alternatives(void) > +{ > + alternative("", "", NCAPINTS * 32); > +} > + > +/* Set a hook so the loading logic in Xen don't consider the payload empty. */ > +LIVEPATCH_LOAD_HOOK(test_alternatives); > + > +/* > + * Local variables: > + * mode: C > + * c-file-style: "BSD" > + * c-basic-offset: 4 > + * tab-width: 4 > + * indent-tabs-mode: nil > + * End: > + */ The second half of the patch (new testcase) is all fine and good, but should pass with patch 2 in place?  I'd suggest splitting it out. ~Andrew