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Wed, 22 Mar 2023 13:13:08 -0700 (PDT) Date: Wed, 22 Mar 2023 14:13:03 -0600 From: Ross Zwisler To: Steven Rostedt Cc: Ricardo Ribalda , Eric Biederman , Philipp Rudo , linux-kernel@vger.kernel.org, kexec@lists.infradead.org Subject: Re: [PATCH] kexec: Support purgatories with .text.hot sections Message-ID: <20230322201303.GA2979303@google.com> References: <20230321-kexec_clang16-v1-0-a768fc2c7c4d@chromium.org> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20230322_131314_530632_D923984D X-CRM114-Status: GOOD ( 30.11 ) X-BeenThere: kexec@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "kexec" Errors-To: kexec-bounces+kexec=archiver.kernel.org@lists.infradead.org On Wed, Mar 22, 2023 at 10:34:46AM -0400, Steven Rostedt wrote: > On Tue, Mar 21, 2023 at 12:49:08PM +0100, Ricardo Ribalda wrote: > > Clang16 links the purgatory text in two sections: > > > > [ 1] .text PROGBITS 0000000000000000 00000040 > > 00000000000011a1 0000000000000000 AX 0 0 16 > > [ 2] .rela.text RELA 0000000000000000 00003498 > > 0000000000000648 0000000000000018 I 24 1 8 > > ... > > [17] .text.hot. PROGBITS 0000000000000000 00003220 > > 000000000000020b 0000000000000000 AX 0 0 1 > > [18] .rela.text.hot. RELA 0000000000000000 00004428 > > 0000000000000078 0000000000000018 I 24 17 8 > > > > And both of them have their range [sh_addr ... sh_addr+sh_size] on the > > area pointed by `e_entry`. > > > > This causes that image->start is calculated twice, once for .text and > > another time for .text.hot. The second calculation leaves image->start > > in a random location. > > > > Because of this, the system crashes inmediatly after: > > > > kexec_core: Starting new kernel > > > > Signed-off-by: Ricardo Ribalda > > To: Eric Biederman > > Cc: Philipp Rudo > > Cc: kexec@lists.infradead.org > > Cc: linux-kernel@vger.kernel.org > > --- > > kernel/kexec_file.c | 3 ++- > > 1 file changed, 2 insertions(+), 1 deletion(-) > > > > diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c > > index f1a0e4e3fb5c..b1a25d97d5e2 100644 > > --- a/kernel/kexec_file.c > > +++ b/kernel/kexec_file.c > > @@ -904,7 +904,8 @@ static int kexec_purgatory_setup_sechdrs(struct purgatory_info *pi, > > if (sechdrs[i].sh_flags & SHF_EXECINSTR && > > pi->ehdr->e_entry >= sechdrs[i].sh_addr && > > pi->ehdr->e_entry < (sechdrs[i].sh_addr > > - + sechdrs[i].sh_size)) { > > + + sechdrs[i].sh_size) && > > + kbuf->image->start != pi->ehdr->e_shnum) { I think we should also be comparing against the initial value (set ~20 lines above) of pi->ehdr->e_entry, not pi->ehdr->e_shnum. This patch works correctly for me: diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c index f7a4fd4d243f4..967826a42cdd7 100644 --- a/kernel/kexec_file.c +++ b/kernel/kexec_file.c @@ -913,7 +913,8 @@ static int kexec_purgatory_setup_sechdrs(struct purgatory_info *pi, if (sechdrs[i].sh_flags & SHF_EXECINSTR && pi->ehdr->e_entry >= sechdrs[i].sh_addr && pi->ehdr->e_entry < (sechdrs[i].sh_addr - + sechdrs[i].sh_size)) { + + sechdrs[i].sh_size) && + kbuf->image->start == pi->ehdr->e_entry) { kbuf->image->start -= sechdrs[i].sh_addr; kbuf->image->start += kbuf->mem + offset; } Great find. With those 2 quick changes, you can add: Reviewed-by: Ross Zwisler > Shouldn't this be: kbuf->image->start == pi->ehdr->e_shnum) { > > ? > > As you want to only do this update when it's not equal to the initial value. > If this did work, then you may want to make sure that was the initial value. > > Also, please add a comment about why you are doing this check. > > Thanks! > > -- Steve > > > kbuf->image->start -= sechdrs[i].sh_addr; > > kbuf->image->start += kbuf->mem + offset; > > } > > > > --- > > base-commit: 17214b70a159c6547df9ae204a6275d983146f6b > > change-id: 20230321-kexec_clang16-4510c23d129c > > > > Best regards, > > -- > > Ricardo Ribalda _______________________________________________ kexec mailing list kexec@lists.infradead.org http://lists.infradead.org/mailman/listinfo/kexec