64 lines
2.2 KiB
Diff
64 lines
2.2 KiB
Diff
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From 82a962066fb5a41b6dc50476f8676b559ac1edcc Mon Sep 17 00:00:00 2001
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From: Michael Brown <mcb30@ipxe.org>
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Date: Tue, 30 Jun 2020 16:32:59 +0100
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Subject: [PATCH] [efi] Raise TPL during driver entry point
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As per commit c89a446 ("[efi] Run at TPL_CALLBACK to protect against
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UEFI timers") we expect to run at TPL_CALLBACK almost all of the time.
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Various code paths rely on this assumption. Code paths that need to
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temporarily lower the TPL (e.g. for entropy gathering) will restore it
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to TPL_CALLBACK.
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The entropy gathering code will be run during DRBG initialisation,
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which happens during the call to startup(). In the case of iPXE
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compiled as an EFI application this code will run within the scope of
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efi_snp_claim() and so will execute at TPL_CALLBACK as expected.
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In the case of iPXE compiled as an EFI driver the code will
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incorrectly run at TPL_APPLICATION since there is nothing within the
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EFI driver entry point that raises (and restores) the TPL. The net
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effect is that a build that includes the entropy-gathering code
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(e.g. a build with HTTPS enabled) will return from the driver entry
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point at TPL_CALLBACK, which causes a system lockup.
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Fix by raising and restoring the TPL within the EFI driver entry
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point.
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Debugged-by: Ignat Korchagin <ignat@cloudflare.com>
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Signed-off-by: Michael Brown <mcb30@ipxe.org>
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(cherry picked from commit 2ae5d4338661b65c63eb5cb1a96e5b803fe7d620)
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---
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src/interface/efi/efidrvprefix.c | 9 +++++++++
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1 file changed, 9 insertions(+)
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diff --git a/src/interface/efi/efidrvprefix.c b/src/interface/efi/efidrvprefix.c
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index 4fbb19ff..a8ef6673 100644
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--- a/src/interface/efi/efidrvprefix.c
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+++ b/src/interface/efi/efidrvprefix.c
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@@ -34,16 +34,25 @@ FILE_LICENCE ( GPL2_OR_LATER );
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*/
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EFI_STATUS EFIAPI _efidrv_start ( EFI_HANDLE image_handle,
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EFI_SYSTEM_TABLE *systab ) {
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+ EFI_BOOT_SERVICES *bs;
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+ EFI_TPL saved_tpl;
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EFI_STATUS efirc;
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/* Initialise EFI environment */
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if ( ( efirc = efi_init ( image_handle, systab ) ) != 0 )
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return efirc;
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+ /* Raise TPL */
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+ bs = efi_systab->BootServices;
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+ saved_tpl = bs->RaiseTPL ( TPL_CALLBACK );
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+
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/* Initialise iPXE environment */
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initialise();
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startup();
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+ /* Restore TPL */
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+ bs->RestoreTPL ( saved_tpl );
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+
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return 0;
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}
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